Ahh - and let's not forget the "open" composition vs. the 'closed" composition - the open leaves a bit of the subject off frame making the viewer wonder what lies betond (great for those shots that you want to convey the felling of "never-ending" - whereas closed compositions encompass(sp) the entire concept of the photographer (as in, this is what it is - take it or leave it)

Rule of thirds - great starting point. I've seen too many landscapes with the horizon right down the center. Some people will say "I did that because it's an interesting sky" - and try to incorporate a barn or something meant to be the subject of the photograph. My opinion - decide what's the subject of your photo - interesting sky or barn...? - trying to incorporate the both disorients the viewer....("Great shot of a cloud formation....or is it a barn...?)

Photos need (in my opinion) to have a single, easily defined subject - with some supporting elements, but not so strong as to compete for attention)

(Keep in mind - these are strictly MY OPINIONS - not by any means to be considered statements of FACT)