The main issue is ladder safety.  Consider getting a ladder stand-off like the one pictured.  A stand-off has two rubber-tipped arms that extend on either side of the ladder and rest against the roof or siding.  In addition to providing stability,  they won't damage the gutters while you're cleaning them.  Shop around; the Ladder-Max Standoff Stabilizer is about $80 on Amazon.com. 

Be sure the ladder is angled properly away from the house.  Follow the 4 to 1 rule:  for every 4 ft of ladder height, angle the ladder 1 ft from the wall.

Wear gloves for the job.  You can pick up a gutter scoop at Home Depot or your local hardware store for about $5. 

Start by cleaning the downspout, and hose down the gutters when you're done to ensure the water is running out smoothly.

While you're up there, check that the brackets aren't loose and seal any leaks with gutter caulk (while the gutter is dry).