Consider practicing some serves with an especially heavy "training racquet". Without a decent progression in your service motion (kinetic chain, blah-blah-blah...) your arm won't be able to reproduce a decent serve for very long. A hefty racquet can force you into calling upon your bigger muscles (legs and core) to drive your overall motion over and over.
DO NOT try this in competition where you can't monitor yourself nearly as well as a practice setting. It can also be helpful to repeat several practice motions with a heavy "trainer" before even trying to hit a ball. Comfortable tempo is vital for a solid serve, even a kicker.