I've been 'caught' short before; my first three years of window cleaning were a nightmare when my tax bill was due paying, so I started paying by standing order and it hasn't been a problem since.
I've got a good idea what my tax bill will be (

), I divide that figure by 12, add a bit onto it, and then pay that figure everymonth.
I'm in credit with the tax man!
I also know from experience that Christmas is a worry when you're skint, so we start preparing for Christmas in the Summer. The only presents left to buy is from me to Wor Lass, but the 24 hr garage is open on Christmas eve, so she'll get her usual 5 litres of engine oil and a 2010 AA Road Map. Sorted!