I reckon you've got to get an add into the phone books (Yellow Pages and the Thompson Local) and keep it there for at least three-or-four years to get commercial work; and be patient.
However, within six months of starting window cleaning we picked up the Hilton Newport from a Local Pages advert (but that's another story).
Anyway, we've picked up two nice jobs this year, both into a three-figured-sum (okay I'll say, 'cos that could mean £999); one at £130 and one at £140 from previous years entrys in the phone books. I've also got a third commercial unit 'in the pipeline', but that is from a contact from Wor Lasses running club.
I stopped advertising in the books about two-years-ago, things were financially tight at the time, but will start again.
And there's always the element of luck; I picked up a nice £70 pub not so long-ago; just by wearing a sign-written T-Shirt and was asked to quote while I was shopping in Tescos, and also my local Spar at £15 a week which is a 'gift'; very quick and easy.
I also did the 'mailshot' thing a few years ago; it was quite a lot of effort; but received only one quote from it, and I didn't want the job.
The phone books are the best bet though.