Use a narrow nozzle attachment to direct the air flow along the gutter to blow the leaves out of the gutter. Work down the length of gutter until all of the leaves are gone.
Set up a ladder along at one end of the gutter. Position the ladder on flat ground so it rests securely against the house. Attach the narrow nozzle to the leaf blower before you climb onto the ladder. If the leaf blower is electric, plug it into an extension cord with enough length to allow easy movement. Position the cord so it doesn't wrap around the ladder.
Climb the ladder carefully with the leaf blower in hand. Position the nozzle so it points into the gutter. Turn on the leaf blower to direct the air into the gutter. Reposition the ladder as necessary to move down the length of the gutter.
Another option is to buy a special attachment kit for the leaf blower designed to clean out gutters. These kids include lengths of straight tubes and a curved tube. When you attach the parts, the kit extends the length of the leaf blower so you can work from the safety of the ground. Hold the leaf blower so the curved end piece goes into the gutter. Turn on the leaf blower so it blows the leaves out of the gutter.