Concerning the center, here is a game:
[Event "Kear's Ency., p.45o"]
[Black "Dixon, W."]
[White "Bryant, W."]
12-16 23-19? 16-23 27-18 11-16 22-17 16-20 24-19 9-14 18-9 5-14 25-22 8-11 26-23 11-15 30-26 15-24 28-19 4-8 17-13 8-11 22-18 14-17 21-14 10-17 19-15 11-16 15-11 7-10 18-14 10-15 1-0
The first clue to what is going on is the second move, which is a loss. Look at the position four moves from the end, and you will see what looks (at first glance) like a dazzling center for White. Lesson #1, the future of this position is more important than the looks of this position. Lesson #2, mobility is more important than looks. And here, mobility is more important than a "strong" center. White is not completely immobile, but some study should convince you that White is losing. It did take a little creativity on Red's part to allow White a strong-looking center.
About the back row. Imagine that Jim Grandmaster (in my dreams) plays 3-7 sometime in the opening. He very probably made that move because it was a familiar move in an opening variation that he had studied for many hours. He has not chosen this move, he has chosen this opening variation, and is aiming for strong future positions.
Sometimes moving a piece off square #3 (or some other back row square) is very tempting or even forced. Maybe the piece on 3 is needed for some task. An example is the most popular line of the Glasgow (11-15 23-19 8-11 22-17 11-16 24-20 15-24 (or 16-23 to same) 20-11 7-16 27-11 3-7 28-24 7-16 24-20 16-19 25-22 4-8). Red has mutilated his/her own single corner; it looks terrible. But a little study shows that White will not begin to king in that single corner anytime soon, and Red still has the advantage. Again, the future is more important than looks.
So, how do you make decisions about the center and the back row? Easy (not always), you use your knowledge of the opening variation being played, and you use thought (study of the position), experience, and judgment. Experience and judgment come from hard work, sorry.