It's pretty obvious that black's plan should be to develop the kingside pieces and expand on the queenside, but what is the best way to go about that? First I think I need to look at things from white's perspective.
What did white do last move, and what does white want in the position? Well, if I was white I'd be struggling for a plan. He has more central and kingside space, but with the queens off the board, I don't see much of a way to attack with it. I'd probably try to move the c3 knight and bolster d4 with the move c3, so that after black plays ...c5 I'd be able to recapture with a pawn and also challenge the c-file. That could be wrong, but if I was white that's what I'd do. So what was the idea behind white's last move? Obviously he wants to develop and likely castle (maybe not castle?), but why put the knight on e2 instead of f3? I'm trying to figure that out, but I bet he wants to be able to play Ng3 in the event black plays Nf5.
Now, what should black do? As I mentioned earlier, queenside expansion is the obvious idea, as is untangling the kingside. What's the best move order and piece arrangement to achieve this? Let's see. I want to play 10...c5, but right now I don't like giving his knight the b5 square. After something like 10...c5 11.Nb5, black is having some difficulties developing with the weakness of the d6 square. Plus, white can play the knight back to a3 at some point which allows c3 to strengthen the center, or white can play c4 to mix things up and get some play there. I don't like that, so I think 10...c5 might be too early. Plus, the queenside expansion can't be prevented, so there's no need to rush it too badly.
I'm intrigued by 10...Nb4. Black has to stop the fork threat and protect the pawn, say 11.Rc1, then 11...c5. If white tries 12.Nb5, then black has 12...Kd7 followed by kicking the knight back with a6 next move and black has some central pressure.
Black can also try something slower like 10...Ne7, followed by seeing how white reacts. I've seen some plans for black in other advance variation lines with a slow queenside buildup with ...b6, ...Rc8, and only then ...c5. The idea is that ...c5 isn't getting stopped, so might as well position your pieces as best you can before doing so.
After calculating a bit and doing something thinking, I'm going with 10...Ne7. If white just castles, then I'm playing 11...Nf5 and that piece looks beautiful. If white plays 11.Ng3 to defend the f5 square, then that knight isn't particularly well placed and the queenside play rolls on. And if black takes the knight with 11.Bxe7, then white has helped black develop and can play ...c5 very quickly.
Sorry for the ultra long post, just getting all my thoughts out. If y'all couldn't tell, I'm having trouble deciding on a plan. Good thing this isn't a G/30