Thanks for the suggestions everybody. Although I've never gotten higher than rank 8 in constructed, I want to give arena another few tries. I did some research on the rewards, and some look very good... but that's always dependant on performance!
I'll give it a shot, but personally, arena feels kinda like this weeks tavern brawl in some ways (but you would know what cards you have).
A lot of good advice is given above. All I'd echo is, you aren't going to get better by not playing.
If you can get good at Arena the rewards are excellent for a player who's still building their collection so although you're not seeing instant gains you will in a very short space of time.
Get stuck in!