I have just had to build my business so i hope my advice helps.
I have always found if you do main roads and villages you can pick up work quicker.In my experience everyone hits the common easy estates(less walking for them,they they speak to more people ) so although you will pick up work you may at times,have to work harder for it.But there is no gol;den rules so thats only my opinion.Business is everywhere if you are diligent and hard working you cant fail.
Do not underprice yourself.We have a minimum charge of £10 per house,no matter how small it is.Price high rather than low,you will only dump low price work later down the line.Do it right from thge beginning.It is better to work one house whilkst others have to work 2/3 in the same time.Market yourself on quality of service and you will be ABLE TO COMMAND HIGH PRICES.
I will be putting more free resources on my website over the next few months,Please feel free to check it once in a while for new information on building / marketing a window cleaning round/ business
http://www.premiercleaninguk.com/index.html