Strength training can make you slower but if done correctly your speed will remain unaffected and your mass will go up along with your grappling abilities. Brute strength can get you out of situations that would be basically game over at other times. There isn't much to it. Well here's the basics, if you repeatedly lift something heavy you get stronger, lift it with a certain amount of speed and you might get a little faster (See the section on speed). There are two kinds of muscle fibers and if you want to get strong try to work both of them, do all of your exercises not only at various reps but at various speeds to get a more total work out, and one more thing, be sure to work on the toughness of whatever your primary striking surface is, spend some time on a heavy bag or something, otherwise when you punch some one your wrist may buckle.
Long and Short Power
I recommend reading the article on this in Inside Kung-Fu January 1999 edition, it was also re-printed in "Ultimate Training For The Martial Arts"
Place a pillow or sack or beans against a sturdy wall. Stand at very short range where your body is only about a inch or two away from the wall and with your right hand at waist level and the bag at waist level as well. Press into the bag with your fist using your arm and the pivot from the hips but do not lean into it. Press hard and hold for 30 seconds or so. Take a step or so back and do it again, keep doing this until you are at a distance from the bag that make not leaning into it difficult. You should have a very short, short, medium, and long range area. Repeat this exercise with the other hand. Keep this up for several repetitions. After awhile add more time to your movements and more repetitions. As the title implies the builds long and short power. This is good for moves like the "One inch punch" and some of the poison hand techniques.