Rules of third - imagine the picture is divided into 9 sections, 2 lines across and 2 verticle. your main subject should falls onto one of these line. Now, rules can be broken and in some instances you should centered the subject, but it depends on the moment.
There is so much you still got to learn yet, sharpness and megapixels means nothing until you have the rest. Sure, getting the photo technically correct is a must, but that is the easy part, the hard part you can teach, you'll have to learn. You learn by shooting lots, experimenting, reading, looking at other photographs.
I tell a lot of people this, read the Learn section in
www.photo.net even the film based topic, it's VERY relevent, it's all the fundunmental basic every good photographer needs.