Gutter Guards Work
If you have trouble keeping small leaves and other debris from clogging your gutters, consider installing solid gutter guards. Solid guards, which cover all of the gutter except for a narrow crack to let the water through, do work well. The lip on the guards relies on surface tension to draw the water down into the gutter, while the solid covering deflects leaves and other debris that would otherwise drop in.
The guards work on every type of gutter, except plastic “C” shapes. Since the guards fit over the gutter rather than inside, they'll cover most standard-size gutters. They're typically attached to the gutter with brackets, with the upper edge slid under the lower shingles.
Screened gutter guards, which are much less expensive and available at home centers, don't work as well. They'll keep out most leaves, but you can expect smaller debris, such as seeds and pine needles, to get through. Screens also make gutter cleaning more difficult, because you have to move them aside to get at the debris. However, in some cases they may be all you need.