I've done it - my advice:

1. You know yourself - be honest, you are only kidding yourself if you cover up etc

2. Don't underestimate how hard it *might* be for you to quit - I tried about 6 times over 18 months

3. Enlist friends and swear them into helping you

4. Avoid situations where you would smoke (the pub) at first

5. Remember that no-one makes you smoke - you have control

6. Don't beat yourself up if you slip - just get back on with it. I really gave myself shit if I got pissed and smoked a fag.

If its a one-off (and not an excuse to blaze a fag) thn let it go and just keep on quittin' remember point 1.