and dont be cheap with your prices, if you get every job then you are to cheap, there are more windows than window cleaners, if you go to fast when you are just starting out, then your own safety can be compromised, so safe and happy cleaning 
Andy
I agree with Andy. Be carefull with your prices.
After starting off and charging too cheaply, I find I'm still suffering in many areas from charging too little to begin with; after three years.
You won't be doing yourself or your customers any favours if you do 'go cheap'.
Also, don't suffer 'bad' customers. Drop them straight away; or if you're tolerant, warn them nicely, then drop them if they mess you about in future.
Don't take any, 'not this month', and the such.
As for speed, stick with it, read plenty of posts here; and it'll come.
When you first start window cleaning your body probably isn't used to climbing ladders; humping buckets of water and ladders around; and your technique will need some development.
Do you know any window cleaners in your area who'd take you out for a day and show you a few 'tricks of the trade', so to speak?
If not, why not ask here?