Good on you.
Don't underprice; you'll regret it later and resent doing the underpriced jobs. If you're in a part of the country where people have cash, charge more; they'll pay it. Customers you gain in winter will stick with you like glue.
Leaflet and canvass together. Work out what frequencies you're going to offer and stick to them. Decide now how you're going to get round your customers and how you'll add new ones (much easier than reorganising later).
Get a notebook. Read through fifty pages of posts on here and make a list of who posts sense. Go back into the past to find good posters. Ian Lancaster might be a good start, though he doesn't post too much now. Then use the search facility to find all their posts and read the lot. Note what they do and take the best of their ideas. However, don't be afraid to improve what they are doing if you are sure you know better - that's how people beat the opposition. Ignore any posts that look like they are just a whinge. (not just when you start, keep up the habit - people who whine about weather and van problems on here just sap your willpower)
Surround yourself with optimists.
Expect to work twice as hard for everything than you initially expect.
When you start cleaning, make sure you're eating enough. It's hard work at the start and when you're low on fuel, your morale will drop. Keep well fuelled by eating and drinking enough.
Finally, the simple bit. If you keep on turning up and you keep on getting their windows clean, you'll not lose many customers and they'll recommend you to everyone they meet.
Vin