I'll take Whitepass's comments further (as a 'semi pro' photographer myself)...
Unless you're really trying to make a statement, try not to centre either the horizon or the main subject of the photo. There is a photography rule called the 'rule of thirds' whereby you divide your photo in thirds both horizontally and vertically, and place your main subjects at the intersection points (where possible). In the case of the last pic, place the horizon very close to the bottom of the pic, as there is no interest in all that black.
Try to lead the viewers eye into and through the pic - in your case by using railway tracks and other interesting objects, you can guide where the viewer 'enters' your pic and where it goes. To understand this, look at a well taken picture yourself (such as by Ken Duncan, Steve Parish etc - they have lots of books in bookshops) and take a mental note of where your eye travels and stops through the photo.
Be aware of your exposure. I assume you're shooting digital; if so (if it has one) turn on your camera's histogram and view it after every pic. You want a histogram that looks more like a 'hill' than a 'valley'.
Get a book on digital photography - there's plenty of fairly cheap ones available at any book shops - and read it! Pay particular attention to composition and exposure (and use of histograms).
Ken Duncan and Leo Meier has a FANTASTIC book available from his website called "Photography Explained" - a small book that covers everything in simple English, and only $14.95 (+p&h)
http://www.kenduncan.com/galshop.php?ms=105&fn=prod&id=2543
I carry that book in my kit wherever I go.
Steve Parish has a great book called Photograph Australia with Steve Parish, another fantastic book that covers all aspects of outdoor photography.