This is one of the most frustrating problems to have. You toss the ball behind you and have to chase it. You can hurt your shoulder and elbow, and dump a ton of serves into the net.
For a consistent ball toss, first let’s go over where you want it to be: about ½ a foot in front of you inside the court, and off of your front toe.
1) Make sure your weight is on your front foot when you toss the ball. I like to lean back, then put my front foot down, roll onto my front foot, and toss as I lean my hips into the court, taking time to coil my whole body as the ball rises to its peak. Once it reaches its peak, I then spring upwards toward the ball and unleash all power in one motion. If you toss the ball when your weight is leaning back, as you move forward to coil, the ball is staying behind you and you will have a hard time coming through the serve with your shoulder properly.
2) When tossing, I keep my left arm straight and relaxed. I hold the ball lightly in the tips of my fingers, almost as if I were holding a wine glass. The tossing arm raises straight up and stays up to increase your vertical shoulder turn. Don’t think about your hand too much, just do what feels natural.
3) When I lean back onto my back foot, I exhale my breath and look to my target. I keep exhaling right up until I toss, to stay relaxed. The same as how a sniper exhales slowly before they are about to pull the trigger.
4) Make sure your shoulders are fully turned before you start your motion. If your legs and hips are turned properly to the side of the court, but your shoulders are too open, the tendency will be for you to toss the ball behind you as you move forward. This is because your body will follow the angle of your feet and hips, but your shoulders are too open to the court, causing you to toss the ball at a different angle. The result is that the ball toss is going one way and your body is moving another.
Practice tossing without hitting. Put a dime where you want the ball to land, and practice landing the ball there.
Visualize where you want the ball to be upon impact, and then simply raise your arm to put it there, then catch it.