Here is a very simple tip if you want to capture nice photos: find ONE subject and isolate it from everything else. That’s it.
Why do you think that shallow depth-of-field portrait shots look nice? It’s not just because of the creamy/blurry background but because shallow DoF isolates the subject from any background distraction. If the background is simple and non-distracting you do not need shallow DoF to get a good portrait shot. Studio shots, where the photographer has full control of the environment, are normally shot at f/5.6 or f/8 or even f/16 because the subject is already isolated.
The main reason why n00bish shots look crap is because beginners tend to cram everything into the frame. This one goes especially to the n00b landscape photographers who would sell their kidneys just to get the widest lens possible. They want it ultra-mega-wide so they could include EVERYTHING in the frame. That’s the quickest way to get a crappy shot. STOP.
Find a subject that you like and have a really good look at it then ask yourself: what is it with this subject that I really like? Is it the entire subject or just some parts of it? Is it because the subject is in a particular environment? If you can’t answer those simple questions then your shot will look crap.
Once you find your subject, concentrate on it. Isolate it from everything. You may have to zoom in or get closer to your target. Do everything you can to single out the subject then take the shot. Now check your LCD and assess if you like your framing. If you think that it’s too empty or too simple then find something that will complement the subject. Zoom out or get into a different angle. Just make sure, when you do want to include more elements in the frame, that they will enhance the subject and NOT conflict with it.
So again, the quickest way to get a nice shot is to pick ONE subject and make sure that nothing else is in the frame. Go out and try it. You’ll thank me.