This is one of the best videos I've ever seen: https://www.youtube.com/watch?v=4yTyOeCCgWc
Also check out John Clayton's Bass Tips, also on youtube.
I just started watching Clayton's myself. They look excellent.
If an instructor is out of the question, I would begin with the integrity of the bass itself.
It's not an easy instrument, but it should not be painful or very difficult to play. You might
want to describe your initial experience with the bass right here on a forum, and get some
feedback right away. The first thing to do is make sure the bass is playable.