I primarily started racing for the stunt races, then I discovered Broughy's videos and got more into racing in general. I work construction during the summer so I am usually better at participating during the fall/winter.
Get started in the crew by checking out this thread. This contains our guidelines and other helpful advice. I highly recommend checking out Slack on there, because it is the best way to communicate with other crew members.
Once you've done that, check out the big list of GTA racing events available hosted by fellow crew members here.