I stopped for 5 years (long story) and when I started back again I was definitely back to newbie level of tolerance. 5 years is a bit extreme for most people though and I don't really recommend it . A couple of weeks should help out a bit though. One thing I've found that helps is switching strains if possible. If I start noticing a toloerance to something that is mostly indica I switch over to a sativa and, presto, my tolerance is much lower.

Cranberry juice won't help much. People drink cranberry juice before a piss test because it is a diuretic and makes you piss a lot. Basically it just waters down your piss to the point where THC levels aren't very noticable anymore. I don't think its going to help much with your tolerance though