The main fundamental thing to get used to is doing the crop math in the other direction with FX lenses. What you're used to seeing as 50mm with your crop body, on full frame, will look like 35mm on your crop would. Having all your glass get wider is the first disconcerting thing you think you're prepared for, that you really really aren't. Particularly when you slap on a telephoto zoom. :D

The other two things you'll end up paying more attention to than previously are likely to be focus accuracy (depth of field decreases, if you compensate for the crop factor difference by getting close to your subject, or using a longer lens), and stabilization. You may end up increasing shutter speed, adjusting your hold on the camera, or using a tripod a bit more.

Overall, though, the main thing to get used to is the vague disappointment you'll find after you've run through all the cool newness of the shiny toy, that your photography skillz essentially remain unchanged, and that it's just a new camera, after all. Maybe one that's a little better on noise, a little shallower on the DoF, a little heavier, a little bigger, a lot easier to handle. But overall, most of the changes you'll run into will be marginal. A stop here, a stop there. It all adds up to a much nicer camera, but it's not going to be a magic pill that instantly turns you into a great photographer, despite the pricetag. There may be a bit of buyer's remorse. Swallow it down. Wait a year. Then try shooting with your older camera again, look over the older camera's images vs. your newer ones, and you'll understand why you did it. :) The time gap is key to showing you how big the difference really is. You may not see all or even most of it right away.