you should be hitting the ball with the palm of your hand if you hit it with the top of your fingers or maybe at your wrist you surely wont get it over the net

Edgar is correct on the hit. I would add that 80% of a successful overhand serve is in the toss. You have to practice the toss enough that you can be consistent every time. I have my players do dozens of tosses before they ever try to hit a serve. Most overhand serves are missed because the toss went off to the side, was too low, or was tossed back toward the server. Once you can consistently toss it and have it land right back in your hand then the hard part is done. Hope this helps!

fist the like madger thing about your serve is your toss so practice that and then move on to hitting it strait down on the ground and work on power and hit with the palm and not with your fingers and do push ups at least once a day so you get more power!!!

What helps me is a low toss..i think it makes it easier.

I'm copying my answer to a previous question that was much like yours. Mos importantly, check out the two links at the end. I thnk they'll help.

Some kids are small, or just lack the arm speed to send over the overhand serve. If you're 13 or under, that may still be the case. I always have my players try to just throw the ball over from the end-line (serving area.) If you can throw it over, you're definitely generating enough arm speed to serve it overhand and you need to work on your technique. If you can't throw it over, start working on that. It'll help develop the strength and coordination you need to serve.

Another key serving point that's missed here is where the toss needs to be. Make sure that you're contacting the ball out in front of your hitting shoulder, not straight above it, or behind it. Start your lift with your non-hitting hand straight out in front and your hitting hand already back. It should be palm-out and behind your ear (like you're trying to hear something far away.) This puts you in a position where you simply need to lift the ball out in front of you (maybe four feet up and two feet out front,) and reach up to hit. If the lift is high enough and out in front of your hitting shoulder you have enough arm swing before contact to generate the speed you need at impact.

I'll sometimes have my team try to snap a towel over their heads to get the feel of generating good arm speed, then snapping from the elbow. You want to make sure that you contact the ball while your elbow is still as high as it can reach. That elbow on your hitting arm shouldn't be coming down until after you make contact, or your technique is just wrong. Whether hitting or serving, it's important to keep the elbow high. I tell players that we snap a volleyball, we don't really hit it. The difference is really obvious once you get a feel for it and it's one of the most common problems I see in young players.

There are several methods of serving overhand, but the overspin and float serves are most common. I'd start by trying to hit a float. Open the hand up big, making contact at the base and keeping your elbow high at contact. You'll get this with some work. Check out this video for a nice demo.

http://www.youtube.com/watch?v=GmXc6qvdMG8&feature=related

And... from my pal Barry Lovelace,
http://www.youtube.com/user/barryluv#p/u/13/yTIjNK_lR6g

jus start really small and work yourself back.make sure ur wristis tight and u swing hard. most important tho is having a good toss that lands in front of ur left foot if ur right handed....good luck!

Try this..... stand at a 45 degree angle. put the ball in one hand on your finger tips. put your arm so it looks like your holding a bow and arrow. hand flat and firm and shoulder back and then you just step place swing!!