We've just bought our first house and are doing most of it ourselves, though a few walls will need fully replastering. (groan)
The best bits of advice I can give is to make sure your starting surfaces are as smooth and clean as possible if you're painting.
We bought a sander to strip the woodwork, it wasn't very expensive, about £25, then cleaned it down and primed it before painting.
It looks as good new, and it made life easier than sanding and stripping by hand, which can take a lifetime.
The old owners black glossed half the house, (just why?!?!) so it's been a nightmare and has involved paint stripper by the gallon, but the hardwork pays off.
If it's an older house pre 1980's paint usually has lead in it so be careful, I'd buy goggles and a mask and open windows and doors.
Also if you're painting, invest in a few good quality foam rollers not the fluffy ones, the foam puts regular paint down much smoother and more evenly.
If you go ahead and do it yourself you'll probably find it very exciting at first, but it's bloody boring after a while. If it wasn't for the savings and sense of satisfaction I doubt anyone would do it themselves. Haha!