Step 1: Ladder Safety
First and foremost, make that the combination of you, ladder, and roof are safe. Start on a dry, sunny day with plenty of light and no slippery wet surfaces. You will be moving the ladder around the perimeter of the house so you'll want to be absolutely certain of its stability, as well as the ground under the ladder and the edge of the roof you're resting it on. When standing on a ladder, never use the top two rungs, keep your hips between the rails, and don't lean over the sides. If your house is one story, you can drastically increase your safety by using a tall stepladder instead. If your roof is dry, sturdy, and not sloped too sharply, you can choose carefully work from the rooftop.
2 Clear Loose Debris Safely
The first step is to clear out all the dry, loose debris from the top of the gutter. Wearing safety gloves and protective eyewear, brush and scoop the leaves, twigs, acorns, and various other lightweight clutter from the top of the gutters. If you have gutter grates, this is a good time to remove them and shake them out. Otherwise, be careful as you clear to avoid sharp nails and screws inside the gutter itself. An alternate method for this step is to use a long gutter cleaning attachment for your leaf blower and do the same task from the ground with air force. This option is safer but noisier.
3 Scoop Heavy or Wet Debris
Now we've passed the part you can do with hands alone and you'll need a narrow scooping tool. Most people will use either a gardening trowel of the correct size or a plastic gutter scraper to avoid damaging a painted surface with a metal tool. Start once again from a low drainage point and work your way around the gutter scooping out the congealed and/or wet debris that is essentially stuck or packed into the bottom of the gutters. Clearing this stuff out is important so that water can run cleanly through the system.
4 Rinse Gutters with a Hose
When you think the gutters are reasonably clean for their purpose, take the end of a long hose up the ladder with you and use a high-intensity spray to blast away the last of the remaining grit in your gutters. While you do this, have a partner check the drain pipes the water is running toward to make sure the drainage system is working correctly. If the water is not able to escape because of an obstruction, it will build up in the drain pipe. then begin to pool in the gutters risking rot, rust, and overflow leading to larger scale water damage.
5 Clear Drainpipe Obstructions
If you do detect an obstruction, you have a few options for breaking it up. From the top you can try flushing it with your pressurizes hose. If that doesn't work, you can work it form the top or bottom with a long handle or a plumber's snake. If the pipe is open at the top, you may be able to prod the obstruction apart with a broom handle or other long tool, or from the bottom you can snake in a thin auger to break up the clog the same way as you would for indoor pipes.
Your gutters are a modest but important part of your home's defense against water damage. However, it's understood that not every homeowner has the time or capacity to spend that much time on a ladder, even only twice a year. For this reason, there are property management services who can do these vital chores for you and help you remember the even longer term tasks like when to inspect your water heater or repaint the exterior.