I don't know how much dry track experience that you have, and much of the above is good advice. If you have a lot of experience, you'll adapt to the rain quickly. If not....
Rain conditions are the best way to learn smooth inputs. You can get away with a lot of harsh inputs in the dry that the excess grip of your tires will hide for you. In the rain mistakes are more likely to generate an "uh-oh" moment which you won't forget for a long time. Besides, you usually don't have to change to a track brake pad either.
Get on the brakes slowly, get off them slowly. This is especially important on your first lap when your brakes are cold and perhaps are wet or have some rust buildup on them. Wind will usually make one side of the car rustier than the other giving you uneven braking on one side. If you don't stomp on 'em, it's easier to correct the angle change with the steering wheel.
On corner exit, get on the throttle gently. Our AWD lets you get on the throttle hard as you exit corners in the dry. This is much more likely to induce a spin in the wet.
If you get understeer, you probably turned in too quickly. Keep that in mind and start your turn in earlier next time and a gentler rate.
Softest setting on sway bars, dampers. Use grease pencil on the side tread blocks of your tires just like you do in the dry to look for ideal rollover. I usually end up about 3psi to 5psi below dry pressures. The sidewalls of your tires are part of your suspension system. Stiffening them will likely make your point of breakaway more abrupt. Yes, some people prefer more inflation for better water evacuation out the sides, but if your tires have even wear across the tread block you're probably better off with lower pressures.
Late Apex Everything:
The comments above about the "rain" line are accurate. Until you feel comfortable taking a corner with a normal, double or early apex, just late apex everything. This often keeps you off the typical race line and keeps your braking in a straight line. It is less likely to have you driving straight off at the exit of a turn, too, giving you extra comfort cushion.
Your front tires will be far more likely to lockup if you keep braking pressure as you add steering input. Even with ABS the momentary lockup will start a slide (under or over.) Best to stop trailbraking for the day. Do your braking in a straight line and get completely off the brake before adding steering input.
You slightly overcooked a turn:
Resist like hell the instinct to lift off the throttle mid-turn unless you'd prefer to take that turn tailpipe first. Just grit your teeth, tighten your butt cheeks and ride it out. You won't do THAT twice in one day.
You REALLY overcooked a turn:
Bye!! If you can still drive it, stay off the raceline as you drive to the pits so that you don't leave grass, mud, or gravel on the raceline for your comrades. Be sure to come back to the pits to check your suspension, tires and wheels for damage.
Going off the track becomes interesting if it has grass run-offs. You're less likely to have your tires dig in and roll the car saving you $$$. Unfortunately, there's also a lot less friction on the grass and it's harder to get it back on track before you hit a tire or concrete wall, costing you $$$.
Have fun with it! It's really the best learning conditions for a driver who already has experience with the basics.