Many players go out on their own and practice serving. The tendency is to work on your first serve and try to make it a weapon. However, a few basic changes to your focus can make both your first and second serve better.
First, try to hit an equal amount of first serves and second serves in your practice. A great drill that I do with my students simulates what you do in a match. After warming up both your first and second serve, start on the deuce side and hit a first serve. If the serve is in, move to the ad side and hit another first serve. If you miss the first serve, hit a second serve on the same side. If you miss several first serves in a row, try hitting a serve that is closer to the way you hit your second serve on your first serve. If you make that serve, try to add just a little bit of speed to the next first serve and continue as above.
Don't be afraid to mix in some second serves on your first serve to help regain some confidence and to keep your first service percentage high. Remember the saying, "a player is only as good as their second serve", and make your goal in practice to improve in this area.
If you are confident in your second serve, you will be more relaxed when hitting your first serve and will get better results when playing the big points in your matches.