Gutter cleaning is usually a nice earner. I use a small plastic trowel from Wilkinsons cut down slightly widthways so that it fits and the front edge cut to make it straight rather than pointed to clear the crud then scoop it into a small bucket suspended to gutter with a proper hook so it doesn't fall off. I also fit leaf guards into down pipes after clearing them as well, they're £1.98 each from B&Q but I charge £3.00 fitted. I always check all ok by flushing water through gutters into down pipes. Never had any problems and customers glad to get them sorted especially after the recent heavy rain.
Always look out for grass growing in gutters and mention that you'll check and clear them.