I think the best way to get volunteer hours is to group your activities together. Find clubs, hobbies, and activities that would give you opportunities to volunteer and give back to the community.
Depending on its activities how it's run, joining a predent club can almost guarantee you a few hours here and there. Our club put together presentations at local schools and helped out at free dental days throughout the area.
I got hours shadowing a dentist who spent a few hours every month doing pro bono work at a clinic. I asked him if I could tag along, and this gave me some more volunteer hours.
I joined a social fraternity that also did philanthropy work. We set up charity golf tournaments, helped fix up a little league baseball field for the community, helped with sorority fundraisers etc. This gives you the opportunity to be social and party (obviously), hold leadership offices, AND receive volunteer hours.
Even your manual dexterity activities can be tied to volunteer work. Many places that offer pottery, sculpture, jewelry making classes, etc. also offer summer kids camps, where you can volunteer your time.
I like killing 2 birds with 1 stone.