At the highest levels, returning a first serve is not an easy task. The smart returners (the ones who tend to win) try their best to get the ball into play, style points aside. One of the best ways to do that is to aim for the center of the court.
A) This gives you (the returner) a lot of room for error. Even if you miss your target, you are in great shape.
B) The server will struggle to get out of their own way if the return is struck with enough depth and/or force. Not an easy thing to deal with, possibly giving you a weak reply.
C) Lastly, the server has no angle off your return to run you off the court.
This is incredibly simple stuff, but knowledge is only a fraction of the puzzle. Returners need to have the motivation to be disciplined and not be tempted to go for the "hero" shot. Attempting to slap a winner off someone's first serve or missing a 2nd serve return by 10 feet clearly shows a rookie player (or one who has checked out mentally because they are frustrated). Keep pecking away and the percentages will slowly turn into your favor, giving yourself the best odds for winning. Nothing is a guarantee, but smart decisions time and time again can increase your odds- that's all you can hope for.
Here are two examples: