Best way to optimize a git repository?

I want to periodically optimize my repositories even if it takes a long time to run the command. Should I do 'git gc --aggressive', 'git repack -a -d', 'git prune', or some combination? The documentation implies that things like git gc will use git repack, but I'm sort of looking for the definitive answer of what I should run to fully optimize my repositories. These are relatively new repositories, all created with git 1.5.5.1.

I also read somewhere (but can't find now) that some of these commands shouldn't be run while other people might be accessing the repository. I want to run these commands on a server that multiple people clone and pull from and push to. Is that safe to do? I'm okay if clone, pull, or push fail during this time (although I'd prefer if they didn't fail), I just don't want to corrupt the repository.