Start a discussion in the ‘Discuss’ forum. It gets your name out there and you can post news/advice/thoughts about a program & link that code in the post which will likely get you more referrals on that. Comment on others’ discussion posts and really interact with the people on the site.
Do exchanges- If you see an active user who you’d like to swap referrals with (ie: you do one of theirs and they do one of yours as a trade), click on their profile and see what you can refer to them, and what they can refer to you. Then, send them a message. Something like, “Hello, would you have any interest in doing a referral exchange?"
Keep your links and codes up to date. If your link or code is out of service, think of all the referral bonuses you could be missing out on!