Here's the link to a good thread about backflipping.
https://www.newschoolers.com/web/forums/readthread/thread_id/255404/
This would be my advice...
The three crucial steps to learn a backflip:
1] build a nice kicker with a good lip into some fluffy powpow- big enough to allow you to get around: not so big that you're gonna panic. don't try it first time in the park.
2] commit. like any spin/flip, you have to really go for it. any doubt or hesitation and you'll eat shit- believe you can do it.
3] tuck. you'll keep in control and keep the flip straight.
I would add to arch your neck to spot the landing, but to be honest the first time will be about timing- the adrenaline will make shit go blurred and you prolly won't be able to spot it...
remember- believe in yourself: when you stomp it you'll feel like the shit, claim it, go crazy, whatever. good luck!