When your serve goes south on you, it's often because of the service toss.
You'll have fewer problems with inconsistent tossing if you follow these four tips:
1. Hold the ball in the tips of your fingers, not the palm of your hand. That way you release it by simply opening your fingers, not by rolling the ball off your fingers to put spin on it and perhaps send it up at an angle instead of straight.
2. When you toss the ball, don't throw it -- lift it into the air. Think of giving it an elevator ride with your whole arm, not just the lower arm (from the elbow).
3. The higher your toss, the more wind will affect your toss. So, do work at developing a serve with a toss no higher than necessary.
In fact, high tosses are less consistent even indoors, simply because you have to toss harder to toss higher, so any slight error is magnified when the toss is higher than necessary.
4. Do you have a sky-high toss and can't seem to make it lower? That's probably because your backswing is long and your brain is compensating by tossing higher to give your arm time to reach the ball. To correct this, check out your service backswing.
Do you drop the racket way down alongside your leg before raising it behind you? That's a long backswing. Notice how far the racket head must travel to reach the ball that way.
Now see how much shorter the backswing is if you just take the racket straight back over your shoulder. Meaning, don't drop the racket at all; just lift it straight back into the "back-scratching" position.
Most players won't be comfortable with that short a backswing, so experiment between these two extremes.
To get your toss lower, go out and hit serves against a wall, playing around with your backswing till you find a comfortable one that allows you a lower toss.
Be sure to pay very close attention to what your racket is doing. (Don't be embarrassed if you even miss the ball because you're paying so much attention to the path your racket takes on the backswing.)
Get a real feel for the path and length of your backswing. Then go out onto a court to hit practice serves.
Be sure to practice several days in a row, so that you reinforce your practice within 24 hours of your last session.