Everything here is really good. Let me add:
1) Having access to a decent sim is a huge help, because you can pause, restart, work through stuff...it's really helpful when you can safely get behind the airplane. Also useful to check out some of the more challenging approaches. My instructor and I had access to a decent Redbird, and I found it was an invaluable tool.
2) Your landings may start to suck. This is normal and you will get through it. Happened to many of us.
3) Does the airplane you're training in have an autopilot? Learn to use it effectively. I think it's one of most safety-enhancing things you can have flying single-pilot IFR. If you have it in the airplane at the time of the checkride, you will be expected to know how to use it.
4) The thing that most instructors (I've worked with a few over the last couple of years) really hammered into me was the way to *think* in IFR...which is mainly asking yourself,
"what are the next two things to do?" This dovetails with the idea of your scan....
5) Don't get wrapped around the axle on holding. It will click. Everyone sweats that.
Once you get your IR, the world of GA really does open up wider. I pretty much file everywhere I go because I find flying in the IFR system *easier* in many respects than flying VFR. And most of the time you'll get vectored for visuals anyway.