rohit1994, there are several things I would recommend to help improve your serve. One is make sure you are as proactive as possible in your learning. Find great references such as good websites with video analysis, Tennis magazine etc. Learn! Figure out what you are doing wrong so you know what you need to do to fix it.
You are saying you jump as you toss the ball. That right there should not be done. As you toss the ball and your toss arm goes straight, your racquet should be behind you, facing down before it comes up into the loaded trophy pose before you swing and your weight should be transferring from back foot to front foot. You only leave the ground during the swing and it's not really a hard jump. You should only be about 6 inches off the ground during the swing. Now if you have an abbreviated serve (Roddick) the racquet never comes down, it just goes from address to loaded trophy pose and you swing. Same timing though. You need to incorporate some spin. Even the pros have some spin on their first serves. They just hit it so hard it looks completely flat. Understand your grips. Continental for your first serve and even slice serve, a more eastern backhand for kick serve. Know your tosses too. Looking at the net pretend there is a big clock in front of you. Toss 11 o'clock (behind your head a bit) for a kick serve, straight up at 12 o'clock for a first serve and 1:00 down the baseline for a slice serve! Give that a try!!! Good luck!