Well, gutter cleaning is just about removing debris from gutters. There really isn't a how-to as much as some things to think about:
Before you pick up you ladder, check for power lines. Check out this list to make sure you're safe!
Start opposite the downspout (this is the high point on the gutter). However, if there is a lot of standing water in the gutter, first unplug the downspout.
After completing a gutter, take a rag and clear off the top rim of the gutter, as well as the side of the gutter that you see from the ground. If you are doing this professionally, this is a must. Often when clearing debris from the gutter, a small amount may fall onto the top rim, or flow down onto the outside facing the ground. Despite doing a perfect job, the homeowner who can't see the inside is left to assume you missed a section and that they are still full. It's remarkable how easy it is to miss a few leaves on the rim of gutters (that you've emptied to looking great). And it's equally remarkable how just a few leaves on the rim of a gutter can make the gutter look full from the ground. A simple wiping with a rag takes care of this.
If cleaning by hand (which you have to do if wet), empty gutters into buckets you've brought up. If this is for someone else, check for woods at the house when giving the quote and ask if you would be able to empty the debris in their woods as described in "How to run a professional gutter cleaning business".
If the roof is walkable and the debris is small and dry, a blower (backpack is ideal) is easy, efficient, and thorough.
Be extra careful when above windows. Know where you are on the house. Despite gutters being overhung past the house walls, it is unbelievably easy to (somehow) end up with wet debris falling onto the side of the house. If this does happen, a simple rag wipe on the siding is good. But if it's on a big picture window, it's a tougher fix. After the job is done, walk around the house to double check no debris fell onto the siding/windows.
Resist the urge to hang the bucket off the side of the gutter. Gutter cleaning is a repetitive process of moving debris from the gutter to the bucket again and again. As tempting as it may be to sweep debris right into a bucket that is even with the rim of the gutter, don't do it. This convenient motion is how debris ends up on the side of the gutter, or (somehow) falling onto the siding. Albeit a longer motion, having the bucket up on the rooftop is the safer bet.
Are you doing this professionally? Check out what i learned about running a gutter cleaning business for more thoughts on this.
What am I missing? Tweet @kujoyardwear and let me know! I'll credit you and add to the lists.