Canvas your own customers first, I was supprised how many of my own customers never realised that I offered guttering and conservatory roof cleaning, one customer had recently had her guttering cleaned out, at a cost of £200 even though its on all my tickets, cards etc that I offer these extra's, I began to push guttering and conservatory roofs a couple of months back and I have gained quite a bit with all this rain we have had.
See how you fair with your own customers first, there normally the easiest because they know and trust you if you have been the w/c for some time.
I also offer a cctv survey at £20, if the Job needs doing I deduct it from there total, if not I still have £20