As somebody that started reading Marvel a year ago.... I found the main Avengers title to be tough going, with a lot of continuity and places and characters I was unfamiliar with that it didn't really bother to introduce, and gave up on it. Avengers Assemble, which finished up a couple months ago, was a lot easier to get into. I've read the first few issues of All-New X-Men, and while there's some time-travel stuff that's a little confusing, it didn't seem too continuity-heavy and I think it could be a good jumping-on point.

Personally, I'll second the recommendation of Mighty Avengers. It's a new team of more... B-list heroes, I guess, so they introduce everybody and there's not a lot of old continuity. I also found some of the new Marvel Now solo titles to be easier to get into. I'm reading Captain Marvel, Ms Marvel, Loki:Agent of Asgard, She-Hulk, and Hawkeye.

If you want to get caught up on older stuff and don't mind reading comics on your computer/tablet/phone, Marvel has a service called Marvel Unlimited, where you can read a whole lot of comics (nothing newer than 6 months ago) for $10/month.