When you arrive at the picnic area, follow the curve to the left, not the right hand parking lot. Then keep moving straight through the lot, until it begins to curve right, then park at the next set of parking spots, you are there! Walk down the steps (only a few, not near as bad as the swimming area, whew!) and there is at least one picnic table down there in a nice shady area. You can tell where the opening to the water is.
After you step in the water, gaze across the lake, and get a compass heading on the pier that is to the right. Go that direction when you begin your dive, and you will find the famous "brush pile." This is the highlight of TSP diving to me, actually. There are many fish that hang out there, including big Bubba Bass, but rumor has it that a fisherman may have pulled him out, I need to go see for myself. One of my most memorable dives was at TSP with Timeliner (it was a cool/cold water day!) just hovering and hanging out at the brushpile for like an hour or so. We became one with the fish, it was just a really cool dive.
There is a good metal platform also, about 20' deep. You stand at the shore entry, go perpindicular to the shore line, following the gravel at first. It is not very far out, sorry to be so vague! There have been ongoing plans to really do some more things for scuba divers out there, but so far I think the economy is keeping that from happening. You can always explore the lake bottom, I think the deepest I've found is around 45'? The swimming area looks like a tempting treasure hunt, and if you're very, very good at braille, it probably is... it will be a total silt-out if there is even one swimmer over there, but I think everyone has to try it at least once...
We've tried only one other area, directly across from Browns point. It was pretty cold that day too, and FooMan broke a fin strap at the beginning of the dive (fortunately Foo is prepared with a sav-a-dive kit won at this very lake!) and the vis was pretty poor, and we couldn't seem to stay out of the grass, got kinda freaky after a while. I would like to try the other end of the lake, possibly the dam area also, but haven't heard any great reports from anyone about any other sites there. For $3 entry fee, it's a nice little dive, but there's not a lot of other things to see besides the platform and brush pile.
Remember, no air fills there, so go prepared. Very nice hot shower house at the swimming area, though!