Welcome Phil! I haven't been doing it long myself, but the progression is fast if you're already pretty comfortable on a bike.
Blue routes -> Smooth, fast, some rocks but generally anyone should be able to ride these trails. No real features, maybe a jump, but everything will be rollable.
Red Routes -> Can be fast and smooth, or technical rocky, or both! just depends on the trail. There may be jumps and some features, but should generally have two paths to take - the chicken way, or hit the feature.
Black routes -> Usually start with a qualifying feature, a big drop of some sort. If you can do this, you can do the trail. Unavoidable features, very techy in places, tight turns, steep etc.
Just build up. One thing that I learned quick is, how much grip your tires actually have, and that rocks aren't scary. don't be scared to chuck the bike around either, get it real sideways in the berms, those tyre side knobbles will keep you on the ground / centrifugal force. Also speed. Don't over do it, build up, but that rock garden you went slow over will be bumpy and a pain to get past slow. But when you go fast, before you've even thought about the fact there's a bunch of rocks there, you're over it and it was a lot easier than going slow.
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