The key to solidifying your serve is to hit a lot of balls. One of the best ways to establish range and directional control in practice is to start serving from a position close to the net. Start serving from inside the service line and then with repetitive success progressively work back to the baseline. Another option is to practice serves using a countdown sequence. Start at a count of X (e.g. 25) and countdown to zero, counting down by one every time you hit your service target and counting up by one every time you miss your service target.
Give yourself only one serve when playing points in practice matches and in competition focus on getting the first serve in and maintaining a 70% or higher first-serve percentage. Develop confidence in a 3/4 pace serve that you can get in no matter the circumstances or conditions.
Establish a ritual (consistent routine) prior to hitting your first and second serves. It could be as simple as bouncing the ball three or more times before hitting each serve. Use the time to settle your mind, clarify your purpose and plan your course of action.
Manage the time and tempo of the match to your advantage (particularly on your service games). Never allow yourself to feel pressured or rushed to hit your serve.
Focus on your toss and tossing arm. Focus particularly on extending and holding up your tossing arm as long as possible.
Likewise, focus on your head position. Keep your chin up with your eyes focused up at the point of contact through the follow-through.
Develop a high margin, topspin or hybrid spin serve. Use the spin for high net clearance and to create an accelerated dipping action on the ball.
Focus on the process of hitting the serve (preferably no more than one or two specific areas of focus such as keeping the chin up and/or extending and holding up your tossing arm) rather than the result.
Be positive. Use positive affirmations and “self-talk” for motivation and to acknowledge good serves and serve sequences.
Stay in the present. Do not dwell on mistakes, missed opportunities or bad turn of events. Deal with the bad bounces, unlucky breaks, etc. by “moving forward and putting things behind you”.