Decent First Serve: I normally use a slice on the BH and a little topspin blocking motion on the FH. I try to just take the strings to ball and follow thru. If really big serve, I will use a slice forehand - like a volley with a bit of a follow-thru.
Weak Serve: I hit a mini-ground stroke. Again, just take the strings to the ball but I will try to hit it with a bit of topspin off both sides. Use full follow-thru for pace and direction.