Here are some things that may help you:
1. Get the sensation of contact and brusing the ball down first . That is, you should be able to throw the ball behind your head and blush the ball into the service box without swinging fast or using elaborate serve motion. Starting on the ad court may help you.
2. Stay relaxed and be smooth. You want to be able to swing fast while being relaxed.
3. Toss into the court and really "kick" foward with your legs vs. letting your body fall the left (assumping you are a righty).
4. Finish the swing by compleleting the followthrough.