It's not only motivation, it's self-discipline. Of course we all have that 'can't be arsed feeling', but you've just got to force yourself out the door and get to work.
Runners often say the hardest part about going for a run is putting your trainers on.
It's the same with window cleaning. The hardest part of the job is taking the ladders off the car. Once I've done that, I'm into autopilot and just get stuck in.
Set yourself a good routine and some targets. Achieve your targets early on in the week/month and slacken off later in the week.
For example; if you plan to earn £2200 per month, divide that up by the number of working days in the month. Say 22 days.
Therefore you've got to work at least £100 pounds per day. If you work a couple of days at £150, then you can start slacking off. If you lose a day to bad weather, then you've got to 'make hay when the sun shines' and work harder.
Try and get ahead of yourself and have a day (or two) off at the end of the month.