The obvious advice is to build up a profile early on when leaving the house, get some PAs under your belt, do a couple of magazine articles, all the usual stuff. Get yourself out there, let people 'get to know you', get your face on screen a couple of times if you can.
Then, ease off a bit, DON'T be in the gossip magazines EVERY week, don't go to every bar opening in town just to get papped for the tabloids. Keep doing the lower profile PAs and earning an income, but don't abuse the public by thrusting yourself at them every waking moment, they will tire of it.
And, for Big Brother contestants, DON'T crash the publicity bandwagon for subsequent Big Brothers, you'll be accused of desperation and living on past glories.