I'll offer the stuff I wished I'd thought of before my first solo (not that it didn't go just fine; it did):
-Relax, because you've done it before without the instructor touching the controls. Say that out loud one time before you take off: "I've already done this!" You can get all "Wow,amazing, I soloed!!" afterwards.
But in fact you will have flown a circuit and landing all on your own prior to that; only real difference is that the instructor was there to bail you out if needed. But it won't be needed, right?
-Expect the unexpected. Do some chair-flying, and throw situations at yourself. Try to think of some surprise or problem you haven't covered in your reading, ground school, or your dual flights. There's bound to be something. If you can't come up with the answers, ask your instructor.
Example: on my first solo trip around the pattern, everyone decided to change runways (no tower,one runway, ops allowed only on one side) right after I was downwind. There was traffic in front of and behind me. My instructor had actually warned me that might happen, but I forgot to ask:
Where in the pattern should you turn around, and which way? The way I chose was "wrong", but it was a safe, conservative choice. But had I thought about it before, or asked, I would have been better-prepared, and it would have been less stressful.
Then there's the stuff I thought of beforehand and used to my advantage:
-Make sure you and the plane are ready (usually the solo follows some dual...so are you sure fuel, oil, etc. are OK? Did you look at that tire after that rough landing before the instructor got out? Do you have to hydrate, or visit the bathroom? Do you just need a quick breather?)
-Take your time
-Use the checklists
-Know the v-speeds, but do not keep your eyes inside too much
-Announce, listen, and look
-Be ready for a lighter airplane. Even if your instructor is a small person, you will notice the difference. It shouldn't be a problem... in fact you will like it. But be aware of this fact as you take off, and as you begin the approach to land.