We do ours March April sorta time. Every other yearish.
Last time we did our price increase if memory serves me correct we were better off by £400 per month. We don't put everyone up just where we think it's worth it or its under priced. Also I think we only lost a couple. Work smarter not harder is the attitude with it.
Don't be afraid of it. We bought some work earlier this year and put it up after the first clean, nobody moaned, and if they did tough, find another cleaner!
We wrote a letter explaining it and reasons with new price. We didn't say if you're not happy call us either, we didn't want to invite a debate about it. This is the price and tough.
Demographics have a lot to play with pricing though. So that £10 semi with 11 windows is 14 miles from another area we do, where a 3 bed detached we charge £12-£15.
As said above do a good job, have a chat to customer turn up regular. The when you put price up they cant argue!
We use the line, although we may not be the cheapest window cleaners, we are insured, regular, do a good job and come recommended. Were in it for the long hall not just as and when!
Price each job on its own merits as well, dont think its a 3 bed semi its £x amount. If you want to do it for £10 say that see what happens, if they say no obv if you want it go in at £8 maybe.