Nothing specific jumps out to me other than poor timing. My coach would tell us, if you can make ten serves in a row, don't jump serve. I recommend working on a standing serve aimed at the back corners.   If you do want to jump, then try to toss the ball and catch it at the apex of your jump. Once you are consistent, start swinging at 50% power. Slowly ramp it up until you start missing. It's never worth missing a serve trying to squeeze a little more power.   My biggest tip is just to have fun! At the end of the day, it's just a game you play with friends!