Writing helpful posts is the main way. Other users can hit the RedCent thanks and it gives that poster roughly 10 Redcents. The person hitting the RedCents reward also gets a minor amount themselves, like 1-2 RedCents.
Here is the older FAQ about them:
I'm intrigued! How do I get more of these RedCents?
Wow, you're rather suggestible. Three ways:
"Thanks" button below a post you like. (Level 2 users only. Earns 2 RedCents each. Please only "Thank" helpful/funny posts.)
"Thanks" when people like your post. (Level 1+ users, i.e. everyone can receive. Earns 10 RedCents each.)
Purchase them. Cheater. (Purchase them on the credits page by clicking "purchase".)
(More info on the RedCent system in our FAQ.) - Link removed, 404 page
Level 1 users: Generally if you help people in the questions forum, or you post a nice little strategy, you'll earn Redcents.
Test/Live update notes or info on upcoming patches
Guides. I've done "Gear Path for Heroic Toons" (requires level 2 access for this forum) which is long and covers gear, spells, quests and links to more info. It earned roughly 100 Redcents on the old forums and 60 Redcents since we updated to this forum.
Creative ways to PL
Interesting tradeskill, quests or other tips
Bugs, though probably not ban-worthy "hacks" like warps/dupes or such. Like a mage spell was bugged awhile back and it would slow your pet instead of haste, that's cool and earned the poster 20 Redcents.
Older members do stuff like:
Share their custom KissAssist ini files
Write "stuff I learned since I started" type guides of hotkeys, KA setups and such
Share snippets of code or their own mods of plugins/macros
Fix broken macros/plugins
Help people with their conditions (this is a big one these days)
Answer lots of questions for newer members
You can also be awarded RedCents by an admin, or at least by Redbot, for something helpful. I had 100 Redcents award recently for something. Probably taking the time to update some older FAQ posts and the sticky ini's page.
Note: Attempting to trade Redcents back and forth with another user, not for actually useful posts for the community, will earn you an auto-penalty. It gets caught pretty fast.