Originally posted by Un-Aru
This is dependent on how heavy you're going and the exercises you're performing. Take the bench press for example. If you're lifting heavy, doing explosive movements are good, in that the weight is not going to move overly quickly, so the correct muscles are still being targeted throughout the movement. If you're lifting too light all that happens is your pecs, anterior delts and triceps are VERY BRIEFLY engaged as you explode out, but in order to control the bar so it doesn't fly away all their opposing muscle groups engage to DE-ACCELERATE the weight. So in actual fact it's more of a back workout. To remedy this, explode out and LET GO OF THE BAR. Obviously for safety you should be doing this on a smith-machine. Or you could super-set a nice heavy bench-press with explosive push-ups (put your feet on the bench) Try these exercises - you'll feel the difference.
Your primary goal is a strength increase. Lifting nice heavy weights for a good 8-10 weeks will help you here. The mass increase will come from your diet, and there's plenty of diet advice on this board. Then start switching to a power workout 6-8 weeks before the season starts to improve explosive power and speed.
For true explosive power though, you can't beat plyometrics.