Also, now that I've gone through this, here's my takeaways that I wish I'd known beforehand:

1. READ YOUR INSTRUCTIONS IN ADVANCE (this includes papers from the doctor directly). I picked up the prep kit the day before I was supposed to start prep and didn't open it until it was "go" time. It was a surprise to find out I was supposed to be on a completely liquid diet the entire day before; fortunately, I'd only eaten a granola bar and it all worked out, but that could have turned out very different. Since most physicians' offices close before your initial dose "start" time, reading the instructions early also allows you to call during normal office hours to ask any questions or express any concerns without debating whether to call the "on-call for emergencies" number. Some medications also need to be stopped up to a week prior, so you'll need to know to do that if necessary (make sure you review your list of meds and supplements specifically with the doctor to make sure there's nothing unusual to stop). My doctor's office also had specific instructions that were different than the manufacturer's, so be sure to read both.

2. Speaking of, make sure you ask about and make a note of the on-call physician phone number and policies for using it if you're not given that information upfront, and don't hesitate to use it if you're having issues. You may be reluctant to wake anyone else up, but that's less of an inconvenience for them than having you show up with an "incomplete" or "inadequate" prep that forces them to postpone or reschedule the procedure (not to mention, extra discomfort for you -- I was miserable and terrified of the idea of having to repeat the prep, ugh!).

3. Ask your doctor in advance if there's any special considerations/adjustments that need to be made to your prep based on the issues you're experiencing. For instance, if one of your symptoms going into this is nausea (like me), swigging a cupful of rather unpleasant smelling liquid likely isn't going to be a cakewalk for you. Ask if you can take/the doctor will prescribe an anti-emetic like Zofran to help you "stomach" (pun intended) the prep (note you'd probably need to take the first dose an hour or so prior to starting prep otherwise it'll be flushed from your system fairly quickly), or ask if you can lengthen the amount of time you're given to drink the prep so you're not trying to gulp it down and can lay down for a bit if you start to feel nauseous before resuming. With constipation problems you may also want to ask about starting prep sooner since it may take your body longer to digest and cleanse your system, and start a liquid diet sooner (although again, I think this would probably help anyone). For diarrhea or nausea, or anyone really, ask if you need to continue taking a dose/complete a dose once you've reached the "goal consistency" of clear, see-through urine like liquid; the on-call physician told me I didn't need to, but doctors seem to have differing opinions on that and it may depend on your specific condition/problem. There are also different prep medications available, and in discussing your particular problems your doctor may suggest a different one or let you choose from a few options.

4. This is not the kind of procedure where you want to enjoy a "last supper" splurge, unless it's a week in advance. Food can hang out in there for quite some time, so it will likely make things "pass more smoothly" if you start a liquid or low-fiber diet several days to a week prior, regardless of what the instructions require. From what I've read this is particularly true if you have problems with constipation.

5. Treat your "bottom" gently from the beginning. I bought so-called "soft" toilet paper, but by about the first "runny" episode I was already incredibly sore and bleeding a little. I had also read and fortunately bought alcohol-free and fragrance-free, hypoallergenic baby wipes, but I wish I'd used those right from the start and maybe avoided or prolonged any bleeding at all. Have vaseline on hand also to use to soothe the area during periods where you're able to leave the toilet -- it does indeed help. So, your pre-prep shopping list (and you want to get it before starting, because you're not going to want to be far from the bathroom once you start) should include: Super soft toilet paper; alcohol-free, fragrance-free, hypoallergenic baby wipes; vaseline; hand soap (preferably something that's also gentle/moisturizing and nice smelling); liquid diet approved items like meatless, noodleness soup broth and apple juice/lemonade/gatorade (be sure nothing is red or blue though, since this can "color" your system in a way that mimics blood); odor fighters (whether it's plug-ins, air fresheners, etc. -- my #2 doesn't normally smell, but boy when you start getting to the stuff way up in there things change); and some form of ventilation (being shut-in the bathroom, sometimes straining, for quite some time did bad things for my nausea and I started to feel faint and overheated at one point -- if you don't have a window or it's not cool outside to open it, and you don't live alone or feel comfortable leaving the door open, a fan of some kind is something to have ready to go).

6. When it gets down to it, this is just an incredibly disturbing experience; you will have strange things coming out of places you'd never expected. Having a general idea of what to expect when you start might help make it less unsettling (although it's still probably always going to be weird to be "peeing" from your bottom).

A colonoscopy will never be something you volunteer to do for kicks, but you can make it more tolerable. Good luck!

Here's some helpful links I relied on during the process:
-- http://www.heartlandqc.com/images/uploads/services/Colonoscopy_-_One__Done.pdf (This has a photo scale of what color to expect your poop to look like from start to finish on p. 12, plus some typical FAQs like what you can eat/drink)
-- https://tearlines.wordpress.com/2013/09/16/some-extra-fun-colonoscopy-prep-tips/ (This has a lot of great tips, and is written in a really fun and frank way that gave me a good laugh when I was struggling)