In order to preserve the life of your roof and eaves, it is always a good idea to clean them out at least once a year.  Twice a year, in the spring and fall, is ideal.  Preserve the integrity of your roof and the structure of your home by nipping future problems in the bud.  This is a good first step.

After the winter season it is common for gutters become clogged with remnants of the roof as well other debris.  In the fall, it is more likely that twigs and leaves are blocking your eaves and this can be a serious problem, because if the water from melting snow cannot run off the roof through the gutters, it will freeze on the roof, eventually causing ice dams.  The ice itself will work its way up your roof and under your shingles.

Start by collecting and removing the larger pieces of debris by hand.  Use a brush to scrub off any pieces that might be sticking to the sides.  Brush and scrub until your eaves are clean.  Giving them a good rinse with the hose washes any other dirt away and leaves them sparkling clean. Many aluminum manufacturers void there warranty on their finishes if the products are not cleaned once a year. Be sure to do this safely, or hire professionals to have the job done.

Source: http://ezinearticles.com/?Eavestrough-Repair&id=3667047#