I don't know if there's an 'official' way of doing this, but I've heard a few different techniques (eg, putting the crock together the night before, then fridging it).
Personally, if I'm going to prep things in advance, I try to take advantage of the extra time, such as by giving the meat a dry-rub.
In theory you can mix the meat and vegetables (as they'll all be cooked to sufficient temperatures to make the meat safe; the problems are when you cook the vegetables for less time) ... but I find that makes it difficult to specifically layer the crock the way that I want to. (I typically put a carrots across the bottom to lift the meat a little off the bottom of the crock).
When it comes time to put everything into the crock, I start it on high for a little while so it'll come up to temperature in a reasonable time, and then switch it over to warm before leaving it to work. (it's possible that the new programmable crockpots do this automatically with 'fuzzy logic' ... I've never tested it specifically).
So, to summarize:
- prep food the night before
- store in containers relative to how you'll want to layer things in the crock. (if not layering, all together is fine).
- don't use the crock as one of the containers in the fridge.
- on the morning of, layer things into the crock about 30 min before you need to leave.
- add the appropriate amount of liquid.
- place the lid on.
- turn the crock on high.
- once the temperature is up to around 130-140°F (57-60°C), switch it over low.
- leave it for the appropriate amount of time.
- switch it to warm if you need extra time before it'll be served.
If you overslep or otherwise need to get out the door quickly ... put the liquid in the microwave to heat up (or stovetop) while you assemble the stuff in the crock, and assemble it while the crock is on low. (you won't burn yourself right away, as it takes a few minutes to warm up). Once the liquid is warm (you don't want it at a boil ... we're looking for near our target 130-140°F / 57-60°C; a couple of degrees over if you have the time), pour it in slowly, working your way around the outer edge of the crock. Drop on the lid, and then go to step #9.