Here is the list of what I think actually makes for good photography and therefore good shots in descending order of importance
1) Shutter Speed
2) Focus (on the subject)
3) After cutting / "light"room effects
4) Aperture & Depth of Field Effect
7) White Balance/ colour setting/ ISO: fiddely wee things of dSLRs/ mFT cameras
Suprised by the order?
The key thing I think that makes the difference between a mediocre amateur shot and a pro shot is not actually composition; it is sharpeness and vividness of colours, or contrast in montone.
Composition through the lens is not always king and I am a devotee of the "light room" cropping blade. As long as a shot has some subject of interest which is sharp ( or not if that is a really unique good blur) then you can crop, monotonise, saturate, sharpen, selectively blur and even photomontage your image, to either rescue a poor composition or find something really eye catching.
My other hobby is sailing and in that sport their is an adage that them whom maketh two mistakes will deserve only second place in a race, while them whom doth have only one wee tiny error will come correspondingly first. In photography if you start to eliminate your mistakes, then you will quickly be able to focus on ( pun there ok!) better composition: ie more interesting shots.
Shutter is King
At 1/250th of a second you are not free of camera shake from hand held shots or even with a rather hefty little mirror on a DSLR like mine, the shock of the mirror mechanism can cause a tiny amount of shake. Also noticeable at say 1/25th on a tripod.
EDIT: Luckily there is a "lock up" anti-shock mirror pre-lift delay to shutter which helps and the higher series E520 and above have image stabilisation (IS) which works well enough to take two shutter speeds down according to users.
On the E450, I find the P (programme) and related Auto (programme with flash), choose too slow a shutter speed : often 200th of a second while being way up at f8: my slowest lenses are zooms which are 5.6, so this is annoying that it stops up and slows the shutter. I notice immediately when the light is down, or at the longer focal legnths, my image sharpness drops.
Try Shutter then you fool Freddie! The problem is that in Shutter Priority you can be out of sensible exposure with a blinking f number as soon as the light changes or you want to go even faster up the shutter dial.
Help is at hand: Sports mode, but this engages the rather poor continuous image sensor focus when using Live View, and does not allow for bracketing: It will at least though, secure you the fastest available shutter speed for a "correct" exposure.
Pro's use faster lenses ( sub f3 in FT or sub f2 where possible) : They choose primes at super wide 20 or 24, then 28, sometimes 35, 49-52 and then 90 - 120 and finally a 200 before you then get into sports and twitcher types of big whites at sub f5.
In the days of film, pro's took far more images than amateurs, thus allowing for some blurred "frames" or imperfections, while often allowing them to get the shot for that series or pose. Now I notice that pro's spend a little more time in set up and checking the camera settings between frames, or series of frames, and I dare say if you canvassed them, you may find they actually take less frames than enthusiasts with dSLRs.
Expensive lenses and top end FF, wider or APS-C type cameras and the Olympus E5( onto ZD Pro lenses) also focus better and faster, and have the best quality lens elements to make the sharpest image plane.
So the kit helps pro's make fewer mistakes.
Focus on Focusing
The higher end systems all offer faster, more accurate focusing too.
I really must say that I miss the old split prism manual focus and find that even some expensive cameras I have tried are not really all that much faster. It is just we are lazy and in the digital world, okay, we want to take masses and masses more frames than before, so twisting the left hand is very passe?
My only advice on focusing is to get used to the cameras focusing choices and settings and find what works on your camera for your style of images and in different situations:
: on the E-450, select spot AF and put it on the centre dot of the three as default, such that you get into the habit of focus-reslect frame. The more complex functions, like hybrid AF and using the AE/AF lock with different settings are also worth learning as I am now: the continuous autofocus does not seem very good to me so far. Face detect is way quicker on the current compact camera ranges from all and sundry than on the E450, but it can be useful. If you have a GH1 or G10 from panasonic, now you can touch screen select what you want to focus on.
Another useful function is M-AF-S which is a combination of an AF followed by a fine manual adjust: in practice it needs to be done on a tripod with 7x or 10x live view magnification: I use it mostly on "macro" close up attempts but also it is of use when you have a disappearing edge:like a door frame, where you want to keep the centre of it in focus so that on say f5.6, the whole frame is in focus with the background blurring out.
MF also has it's place , in close ups, indoor shots in low light and night images, when the "night scene" pre-programme doesn't find anything to focus on.
Bracketing is my favourite means of improving photos and I guess the technique came from pros: certainlky it relates to the experience of running the test strips in the dark room when exposing paper. Pros were and probably still are, more likely to use an external meter to get the correct exposure and then push the emulsion or print, the ISO or the curves now, to get the best from the frames which were taken at the "correct" exposure.
BKT allows you to look at is which exposure is most pleasing for the subject : but further more, you can get around many faults coming from over or under exposure and resulting at sensor - processor level noise.
You can see that you gain or lose in detail, contrast, sharpness-DoF, and over all feel of the image: you can also see which exposure makes unacceptable white-out highlights, noisy-hard black shadows or unwanted noise flecks and pixelation effects in quarter tones.
In other words, you may be able to eliminate noise ( abberrant, coloured pixels) by selecting the shot which is slightly underexposed and "lifting" all the graph to brighten and reveal detail in the three-quarter tones and shadows. Or the converse, an over exposed shot may have a grey feel to it, but capture detail in the subject area the "correct" exposure does not.
BKT is worth starting experimenting on in Programme with ISO AUTO, and the exposure compensation being +/- 1.0 : a whole exposure step, so you can learn what type of shot requires which side of the line ( the camera does vary the ISO in order to bracket down one f stop beyond a certain dark exposure limit) . This was easy on the old needle days: you underexposed for highlights and if you were on transparency films and you could rely on the lab to either get lucky on their test strip or totally mess up a whole roll of Ektakrome for you!
On a tripod with a static scene you can also then work up layers from your bracket in your image software, which add both contrast and detail to the subject.
BKT is the main function I wanted which was not available on a compact camera with RAW file format for under €500. Hence I bought an E450 with a kit 14-42 and the 25mm f2.8 prime ( =50mm in old money 135), which renders the system smaller than the Fuji FinePix /oly 6000s with the biggest zooms.
The noise issues with the FT 10mpx chip can be worked around by bracketing: noise comes in at either end of the scale for any camera- abberant red flecks in both shadows and highlights. Also it comes to happen on some grey tone or quarter tone ( brigth areas which are less light than highlights) that there it is again: noise.
Some of this is associated to JPEG compression- set the camera to take RAW + a jpeg of your preference; if the CF and XD are getting filled, then pump down the JPEG to small-medium-compress for internet use. Finally to get an umissable frame, switch off RAW and go back to Large Fine Jpeg and select ISO100.
If you get the shutter speed right and look at eliminating noise and getting a choice of best exposure, then the next thing to look at is controlling and utilisation of Depth of Field.
This is influenced by the aperture of course, the focal legnth of the lens but also the nature of that particular lens: the 40-150 even at f5.6 gives a very short depth of field, so much so you have to stop it down to deepen it! Where as for comparison, the 14-42 at max mm (=84m), gives a deeper depth of field than the 40 at the same.
Short and super wide angled too vary. But one area which also varies is the sharpness of the actual supposed focal plane at high f stops: this can be so soft as to render them not worth having the f2.8 or 1.4 setting! This affects several FT lenses I will not slander further, and the faster Zuiko OM primes when used on FT cameras ( presumably also a little soft on film!)
BKT is also very useful in DoF experiments, where you want to select a most pleasing fade in and out or when you want to look at light in addition to blur to bring out the best in the subject-background relationship.
Finally here I get onto what you frame with your fancy bit of "enthusiast, pro level" kit!
The only thing I will say tonight, is you have to decide what the photo is going to be OF. What is the subject and how will it differentiate itself, stand out, from the background?
If of course, you are shooting a pattern, or texture, it is kind of the opposite; how to make the whole frame the subject!
The final note on this is that you want to look for the golden zone and any triangle. -shapes or leading S-shapes in the image : I kind of do this naturally but miss out on some which i Kick myself for in the light-room. A tree is not pefectly on the S, or whatever!
The simple things still mess me up in composition: level horizon! But most of my potentially good shots gone wrong are messed up by shutter speed and I know this is the case for many, many photographers!
Practice : Chop Water, Fetch Wood
I would say go out and get the above list in that order or priorities, sorted so that you know when you do go on a shoot or when something is happening and you have a camera on you, that you can very quickly set the camera up and be confident you will overcome user-error, while adapting to the restraints and opportunities of the situation and lighting.
Put the camera on a small tripod and set it to P on ISO400: So take some frames of your table, take some of the objects on the table (without flash!) Set the camera on Shutter, 500 or more with AUTO ISO: Take photos of your house, your car, your spouse, your kids and your dog. Take photos of the view from your window and up and down the street. Focus on each lamp post in turn! Use BKT, go through the settings without too many combinations.
Then move onto BKT shots: start +1/-1 and then move down to -0.3/+0.3.
After some time you may find that you will be clicking not at the BKT function but at the little expo comp button and moving it for your expectations of the condiitions, taking time to alter the frame or more rough exposure settings with far higher aperture settings or faster shutter speeds on "correct" exposure to begin with.