I hope you won't mind some advice from an almost-finished instrument student =) I have had three good instructors along the way. I take no personal credit for any of this.
I use Vibans (
http://www.viban.com/). Love them, but I wear glasses, which make foggles impractical for me.
This sounds like standard bullcrap but it totally isn't. (1) Keep up your scan, (2) When you look down, in reasonably calm air, let go of the yoke, and (3) keep up your scan. Did I mention keeping up your scan? =D If I am not holding heading and altitude, it is probably because I'm fixating.
Also, learn to fly with your feet. Make heading corrections without touching the yoke. Unless there are turbulence induced roll upsets (and sometimes even when these occur but are relatively minor) you can fly hands off if trimmed. This lets you know that you ARE properly trimmed, lets you focus on the panel a bit without being distracted by the yoke, is much easier to make minor heading changes, and will keep your ride a lot smoother for you and your passengers (eventually). Remember that making minor corrections with the rudder means you are actually rolling the aircraft too. You don't need ailerons to roll!
In closing, keep up your scan. It is my understanding having flown with some experienced instrument pilots that even THEY get fixated once in a while.