Paul,
It can be done, just put in the hours and knocking is your best way. Leave leaflets when no one is home.
In 7 months ive gone from being jobless to 260 regular customers, one off jobs coming in that much that i sub work out to my brother to make life easier for myself and still make money.
Tips...
1) knocking is the best way to gain custys - all i say is do you need a window cleaner
2) Leave a leaflet if no one is home
3) Advertise window, conservatory & fascia cleaning (gutters if you can do them) on you leaflets
4) I someone asks for a quote only and says they need to speak to there other half, ask for a phone number and if they dont call in a few days.... give them a bell (picked up loads that way)
5) leave a card / leaflet in shops - had a phone call yesterday from a leaflet my wife left in a shop (10p a week - 4 weeks paid) the woman says its a 'rather large house'
6) do a good job and your customers will reccomend you to friends / family (had 3 reccomendations this week alone)
7) One off jobs come back - my first ever conservatory job i did in my first week came back to me and wants me to do her windows as her w/c is leaving

keep a record of one off jobs, ring them next year
9) You get what you put in - more hours you put into knocking / quoting the more you get.
10) Dont forget you need family time
11) Software helps - i got george the other month (there are others) wish i had got this sooner as it would have made my life alot easier.
12) learn from your mistakes - everyone underprices - take your time when giving a price and get back to them if needs be.
13) Dont offer lower prices - i believe in karma - if you go stealing other windys customers for a couple of quid lower it will come back and kick you up the ass.
14) stick to your price - ive always said my price is what im worth - if they want cheaper, they will drop you for the next person who will give them a lower quote (crap customers are not needed)
15) Read the forum twice if you have to, i spent 3 days reading back posts and slept little. The knowledge i gained was immense though.
16) There will be people who say different things work for them. Try them all and see what works best for YOU
17) Black & white leaflets work great. Something nice and simple. I pay 1p per leaflet when i order 3000 + (A6 / 1 sided)
18) be polite in your manner, i find a smile helps even if you dont feel like it
19) dress code - knocking... smart casual (shirt and tie and they think your a double glazing canvasser) cleaning... you dont need a fancy outfit, just something plain (i have my old companys polo shirts)
20) if you have a bad days knocking and get nothing remember this. I have had a call 5 months down the line from a leaflet i first put out on my first day.
Good luck, you can build a great business
Keep us posted on how you get on