Any ROTC Cadets or Officers went through advance camp (LDAC was the older term for it). Any advice and things you wish you knew?

I went in summer 2017... Don't worry too much about the basic soldier skills tasks. If you don't already feel comfortable with it, they give plenty of time to review with your battle buddies. I'd argue the most important thing to focus on is being a good team player. A large portion of your rating comes from peer evaluations and observations from cadre on your ability to help the people around you complete the mission. Volunteer for details, carry the squad's 240b on the second mission of the day, take the shitty fireguard shift, and try not to complain. Display your confidence in the things that you do know how to do. If you don't know how to do something, ac is a good time to learn. There isn't always a black-and-white answer to everything. Since everyone has different experiences, you'll need to be okay with doing things different than you may have learned them. Make some friends. There's a good chance that you'll see some of them again down the road.

I went to Advanced Camp the first year they changed its name to NALC, which was quite a while before it was re-named again to LDAC.

What others wrote here is essentially true; put a lot of effort into being a team player, because if you succeed while others fail, you haven't really succeeded. It's a combined effort, and too many "Armies of One" are not going to get the job done, and the lesson of that is a large part of what you are supposed to learn. It also means learning what skills others are good at and leaning on them (and formally delegating when appropriate) to do those specialized things, which is a good leadership skill in itself. A "Skill" may be something standard like someone who's good at navigating, but it may also be something more likely to be missed unless you stop to think, like using the detail-oriented person to check that everyone has all the gear they're supposed to, or the one who knows knots to help tie things up, etc.

As for everything else, it's a rehashing of what you should have learned from your last few years anyway. There won't be any curveballs of new material. If your ROTC BN adequately covered the fundamentals, you'll be fine. If they floundered on them, you'll find things a bit more difficult.

Now, since you say you're concerned with Land Navigation, take it from the one guy who disproved the old phrase "Can't spell Lost with out the L-T": know how to orient a map properly to your surroundings, check over your points twice when plotting, learn your pace by memory (both road and brush, but also uphill and downhill), learn how to look "through" a point with your compass**, and make prodigious use of attack points. That last one alone will be like magic for getting you where you need to be, as at camp there will almost never be a point beyond 100m from a good road you can use, or more than 300-400m from a road intersection (which then gives you an absolute map location) and if somehow you screw up you know where to quickly return to so you can re-orient and re-try.

(** I've found that most people never learn this, or at least not properly - looking "through" means that when you're lining up your azimuth, you find a near object [anywhere from 20-200m depending on brush, but further distances help your pace stay accurate] on that line and also a far one [the farther out you can cleanly pinpoint the better]. As you walk, focus on keeping those two in line with each other. That will prevent you from wandering sideways and throwing off your pace. Once you get to the near object, you should still have the far object in sight, but double-check your compass and get a new near object to use, then repeat as necessary.)

Trust your instincts.