first of all, you need to spend a few bucks and get a hopper. your back will thank you and your practice time will be more efficient. I'm not a pro but from countless hours reading books, mags, instructional video, watching you tube videos and helpful knowledgable people on the courts and here at tt, I have come to the conclusion that simpler is better. Balance, throw ball consistently, watch the ball, hit ball with racket in a throwing motion....smmmooothly.
Unless you can do this, all the helpful hints of shoulder turn and elbows up and hip foward and jumping and throw ball in front and spin and pronate and wrist snap will just over load your brain and body.
Get your racket and body into trophy pose, throw ball, throw racket at ball smoothly while keeping good balance- initially forget about where the ball ends up, just make good smooth soild contact. forget about the jumping for now. I have played with tons of older folks that don't jump, or minimally but the ball has plenty of pop. the jump will come naturally, once you have a solid reliable svc motion, you will be able to go after it more.
if you have a few bucks, the james jensen 'ultimate serve video helped me alot starting out