It is very easy to neglect the serve during a practise or hitting session, especially if you have endured a hefty session hitting of the ground. Players often only hit a few token serves at the end of a practise session without too much focus. Make time to practise the serve, start off some sessions hitting serves or devote a full session to serving.  Practise hitting a full basket with a goal for each serve.  Do not make it too complicated or you may lose your rythm. Work on 1 point at a time :-

1. Improving the height of contact - Try to make contact at the top of  the ball toss, often players let the ball drop too low and therefore hit it too late.  Try and hit the ball at the top of the ball toss just as it is about to stop.  This should also help you avoid an excessively high ball toss and should  encourage you to generate good racquet head speed.

When the above becomes natural you could try point 2

2. Try working on more of a knee bend, bending your knees as you get ready to strike the ball,  then push up with your legs as you go up to swing thus directing all your bodys energy upwards and explode up towards the ball.

Good luck