Ask around before you dive some place.
Windy Point at Lake Travis has a pecan forest down below if you get way deeper than a new diver should be.
Stillhouse Hollow and any other heavy boat traffic place should be treated as if there were an overhead. Allot of jet skiers out at a party or something do not heed dive flag warnings. What I mean is that a shore entry should end with a shore exit, and you should avoid going to the surface out in the open water when possible. (For example, to re-find land when you should have been keeping track with a compass.)
Stick around the Swamp Divers forum and come dive when you can and you start to pick up this kind of thing. I am new too, and by no means an expert, but this forum and diving with people here has taught me allot.
I would also add vertigo, and not handling it properly as a hazard. It is (or was for me at least) very easy to loose a reference point and start 'spinning' in all the muck. Focusing on my SPG always helped, gave me something to focus on, and assured me that I had plenty of air and nothing to worry about. Lots of good reading on the forum if you search for it.