I actually remembered to bring and put on my gaiters for a muddy coastal trail once (Olympic Peninsula). That was the year I slipped and sat down rather suddenly in the mud! I scraped off what I could and let the rest dry on the remainder of the trip in. At our beach camp I changed into rain gear and rinsed off my hiking pants and shirt in the surf.

In other words, it's probably questionable whether any technique will for sure keep your clothes from getting muddy! Have a lightweight base layer along to wear inside the sleeping bag. Otherwise, a little good clean mud never hurt anybody! Do have some kind of plastic bag (even a shopping bag would do) to protect your tent from the muddy clothes.