Going to more than one job fair is a waste of time/money. I think the first one was a waste, but I still recommend giving it a shot at least once.
The best thing to do is get the time at a regional and start making mainline contacts from day one.
My job at CAL came out of nowhere and I was not expecting it, after years or building contacts at DAL and AA.
Don't get too caught up in the path to a major, I did and wasted a lot of time worrying about it. Every pilot (100%) that I know that wanted to go to a major and kept their personal and flying records clean all have jobs at majors now. Besides building time and keeping a clean record, the most important thing to work on is making sure that you are a people friendly person and that you can start and carry on a conversation with ease. That will go a long way during the process.