The best and most useful two things I did when I first got back into mountain-biking after being away from bikes for years was 1) signing up for a race two months from when I bought my first bike (gave me something to work for) and 2) went to my local bike shops and found out who had weekly 'shop rides' and joined in. I quickly made friends with guys I could ride with and learned everything else along the way.
I also would show up at a trail head on a Saturday morning and when a small group was headed out, I would say 'mind if I tag along?' and was never, not once, told no - but not everyone is up for hitting up strangers at a trail head.
Best of luck and see you on the trails - if you're ever in the Western US that is