Depends whether its a points or 5x5 H2H league - for points, picking 2 start pitchers with decent matchups to get a lot of points, especially for wins, is a tactis a lot of people will use.
In daily 5x5 leagues, if their is no Max IP per week set, some people will try and start as many pitchers as possible to try and win W, K, and some will use relievers almost exclusively to win saves and the ratio cats.
For hitting, you want consistent players:
2 Years ago, I had Shawn Green in a CBS pts H2H league, he had been slightly disappointing up to then, and I read that he had been playing with an injured hand, which explained why, so I benched him for the next week...
Unfortunately, that was the week he hit 4 HR's in one game at Milwaukee and seven, I think, in the week, and put up some ridiculous number of points.
After looking like an idiot for benching him, I kept him in my lineup for the rest of the season, even though he didn't put up very good numbers.
Bernie Williams used to be the ultimate consistent H2H player, but his knees are falling off now - you just have to avoid streaky players as much as possible.