step one thrash the life out of it to clean out exhaust
Every day, every day

.
Actually, less so now that I've moved down to London. I'm not too worried about the emissions -- they were fine last year, and not a lot's changed. It's other stuff that's starting to cost money -- I had to replace the brake discs a few months ago, and I'll need to get the gaiters done before the MOT this month.
And, since I don't have a clue how to do all of this stuff, that means more expense.
It's not helped by the fact that while doing a U-turn the other week, I managed to kerb the left-front wheel and take out the sidewall -- took the tyre almost completely off the rims. That tyre was a bit dodgy anyway -- I had to keep topping up the pressure every week.
Fortunately, I was only doing about 3mph, so no harm done. Unfortunately, my spare was under-spec, tread depth-wise, so after the AA man replaced the punctured tyre with the dodgy spare, I had to drive directly to the tyre place for two new tyres.
So, on the bright side, my brakes and tyres are all OK for the MOT.