Overthinking is no good, but underthinking can be pretty bad as well.
First, make sure you know what you're getting yourself into, then make up your mind about whether you want to go for it or not. Check out the curve of the jump, the landing, etc. If the jump is way bigger than what you're used to hitting, has a very different shape, or anything like that, you might want to concider not going for it, especially if you're feeling uncertain. (If you're not willing to get hurt, I would think this is the way to go)
Then, find the right speed. Depending on the jump, it might be better to be going too fast rather than too slow. Evaluate. If other people are hitting it, do what they do. Pay attention to their speed, and if they pop of the lip or not. If you're really uncertain, you can even follow someone who knows the right speed down the in run to get a feel for it.
Once you've done all this, you should be ready. Make sure you've warmed up and ready, hitting a big jump is not the first thing you want to do in the day. Consider the weather, maybe?
You should feel ready after doing all this, but if you don't, it's time to question whether you want to do it or not. Give it some time, do it another day. Build up your self esteem on smaller jumps.
For the first hit, personally I would recommend a straight air (with a grab), but if you're confident, 360's work as well.
This works for me, but if it sounds stupid to you, crank your tunes, smoke whatever you might have handy, hit your head to feel numb or whatever.