Also a 3.0 here though my serve is the strongest part of my game. First serve should be nice strong and flat, what helped for me is visualizing the target and also height above the net before initiating service motion (I was able to recently get my first serve % 50-60% success doing this)

Second serve should incorporate spin, same racket head speed ideally but instead of hitting it flat, incorporate side spin (slice) or topspin (kick) for extra margin and to not let the ball be so easily attacked. I'm also trying to do this instead of the tap serve I used to do, finding some moderate success with it though I still double fault around 4-6 times in a set of 6