I generally use some kind of perfunctory outline that is chapter-by-chapter, so that if I get distracted I at least know what “goes next”. Without an outline, I would not have been able to have completed last year’s Nanowrimo novel, although about 2/3 of the way through I found the characters taking over and going outside of what I’d planned for them, the little buggers. Not that that was a bad thing at all!
If formal outline leaves you cold, try creating more of what I’d call a “clotheline” outline – you know how it begins, you know how it ends, you know a few events along the way, but you don’t have the entire laundry list on display, and sometimes you switch the overalls with the undies.
Some kind of outline also keeps me from using so-called “writer’s block” from stopping me – I always have something to look forward to writing.