A question about match-ups

[Fez]

I know of course, that the character your opponent plays will effect the behavior of the ball to some extent so one must adapt to opponent's character. But my question is how much?

That is, how much must I take into account opponent's particular attributes? If i play I guy who has a lot of topspin, what should I do that is drastically different, if anything? Or if ball is flat?

Another question: What character attributes should one be especially aware? Which ones should I beware to alter my play to? Or am I reading into the game too much?