When I did my DE last Spring I went with stock tire pressures then checked them after each run. My goal was to keep them around 40psi while hot. This required removing air from the rears several times.
I would agree with the advice provided:
1) Look Ahead! Harder than it sounds but it makes a huge difference in how you drive. Also helps you to see the flags
2) The smooth thing is good advice - no sudden jerks of steering wheel, slow throttle and braking. So don't come out of a turn and floor it. If you fail to be smooth you can upset the balance of the car, weight distribution etc...
3) Going slow will make you faster!! Take your time at first and understand the lines etc.. and gradually increase speed. If you get uncomfortable or start missing your apex, slow down again.
4) Be aware of your mistakes. After every turn I would mentally evaluate what I did, apex too early or too late, or missed brake zone or braked too hard etc.. When you recognize what you do wrong you can work to improve it on the next time around. Avoid the early apex, if you miss it go late
5) Don't feel 'pressured' by other drivers. There will be faster cars, let them pass and don't worry about it. It is easy to start getting an ego and want to keep up with more experienced drivers.
6) Have your friend review the basics - hand position, rev matching, what an apex is, where the brake zones are etc.... This might be stating the obvious, but don't brake while you are turning, accelerate through turns brake while you are going straight.
Good luck, you will love it.