My biggest piece of advice: Don't ask about it and contribute to the community.

I never asked to become a mod. Forums where I mod at, the admin or another mod approached me...based on my interactions with the community. Asking to become a mod is usually a sure fire way to not be considered. Most times, people who want to become mods end up on power-trips. The quiet, unassuming people usually make the best.

Just do your thing and if someone thinks you can help, they'll probably reach out. But asking, sucking up, etc. usually does not work in a quality community.