Not knowing the customs of your area, I can only speak of mine.
Around here, the speach to the groom is somewhat of a roast. Albeit a friendly roast. Do not mention ex girlfriends, sexual conquests or illegal activities. Everything else is fair game. The point is to embarass the groom, but keep everyone smiling.
Keep it relatively short. No one wants to sit there for fifteen minutes listening to the stories. Five to six minutes, is perfect. Any more, people get bored, any less you come off insincere.
Be funny! If he was in an accident while driving a forklift, and no one died, tell the story. If he slept walked into his parents room, and peed in a dresser drawer, tell the story. If girls at KFC like him, and used to give him free chicken, and now he calls his belly "Pure Charisma" tell the story. All of these have been used in my life, and they all brought the house down.
End the speech with sincere thoughts and feelings about him, and how you're life is better with him in it. Tell the crowd he has good in taste in friends and even better taste in the woman he has chosen to spend his life with (even if you can't stand her). Wish them Congratulations, and the very best in the future, and ask the crowd to join you in a toast to the groom.
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