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You might also look up the "rules of composition." Bear in mind that they are not really engraved in stone rules, they're more like suggestions. There are a lot more rules in composition than the rule of thirds and leading lines.
=Yangosplat has given you a link to a tutorial on the rule of thirds and leading lines, and I have not really read it, but nearly every one of those tutorials fails to mention that you should more often use the "rule of halves" on a symmetrical composition (put the eyes on the upper horizontal bar, but the body goes nearer the middle the more the subject is turned toward you and the more symmetrical the subject appears.
Also, when Yangosplat said "the quality of the photo does not matter as much," that means that there is a narrow margin of error, when it comes to exposure, and it is pretty damned slim, but you don't have to be perfect to have a good photo. Of course the nearer you are to perfect, the better things are going to be, so you do have to try, and pros bracket like hell (shoot one pose at several different exposures) so they get it right.