Plenty of good advice here. FWIW, I have a few personal things to address before sending first solos - or indeed any solo.
1) Try to separate the errors into safety (eg carb heat not used before throttling back, pre-landing checks ignored, etc) and less important (DME. Doesn't actually matter when you turn it on, it's just nice to have it on a few seconds before you actually need it!). Guess which ones give me more concern...
2) Plan ahead. Have a quick think about the takeoff and crosswind turn before you make a departure call. When climbing out on crosswind plan the level off, downwind turn, and checks. Talking of checks, get them started as soon as you're sensibly level and trimmed - don't wait until you've made the downwind call, ie give yourself a few seconds approaching the end of downwind to relax, rather than relaxing early and then being pressured.
3) Do as little as possible! Don't be lazy, but if the speed, picture, configuration and power setting are right on final then don't do anything until the flare. Few things more annoying than someone fiddling all the way down final approach and messing up a perfectly good circuit because they won't sit still... My usual cure for this is getting the student to trim at the top of final and then let go of the yoke. Next time they do anything is to flare!
Last but not least... It's hard to do, but try to ignore the cost for a lesson or 2. Go along determined to have fun rather than to set yourself a target. I would far rather have to convince a student of their ability by getting out on the taxiway (once so far!) than have to damage their confidence a bit by telling them that they're not fit solo when they've convinced themselves after a couple of circuit sessions that they've hacked it. Sad but true. It's supposed to be fun!!