1. The toss. Tell yourself to catch bad tosses, and force yourself to. Often I just want to hit the serve so I'll go for it on a shitty toss, but if you have the right toss you will hit a good serve if your motion is sound.
2. Legs and stomach. I have a powerful first serve because I bend my knees and then jump up and thrust my whole body forward, trying to emphasize abs area instead of just arm, so I'm putting most of my weight behind it.
3. Make sure you have a good grip. Continental is the way to go but takes time to adjust to. Still, there is a clear difference between any continental grip and one where that allows you to get a very natural wrist snap. Just mess around with your racquet a bit to find what feels right. And make sure it doesn't strain your wrist, because that is an easy problem to have as well.
In terms of mechanics it's hard to say, but try to find what feels natural for you.
Does anyone have advice on second serves though??? My first serve is very good and my second is decent when it works, but I go through patches where I just get the yips and can't get a second serve in the court. Even when it works, it's sort of just a softer version of my first serve that I try to get deep in the box rather than a shot I can actually depend on