You can promote balance transfers in a number of ways. The most obvious is with simple comparison marketing: Spell out for the member, in black and white, the advantages of your program compared with those of the big national banks. Show them how much money they can save in interest, fees, rewards, and more. Money, after all, talks loudest.

Try creating a promotional offer with special incentives for balance transfers. If your card program includes rewards points, for example, consider kicking in a substantial number of bonus points for every balance transfer.

Alternatively, you might look at partnering with a local merchant to create a cross-promotional marketing program. This way, you can grow your card portfolio while contributing to and supporting the local economy.

2. Target New Borrowers

By the time you close a new loan – whether it's a mortgage, auto, or some other type – you already know the borrower is a good credit risk. You've pulled their credit reports and you've analyzed their income. You also know this member is more inclined, and qualified, to borrow from your credit union.

Each time you close, then, issue a credit card to that member along with their new loan. This circles back to balance-transfer marketing, as well. Explain why it makes sense to use your card instead of someone else's, and how they'll benefit from transferring the balances from their other cards onto yours.

3. Higher Limits

Today's consumers are more credit savvy than ever before. They know they need to keep their credit card balance at or below 40 percent of their total card limit — or risk negatively affecting their credit score. At the same time, increased spending helps grow your credit card portfolio.

So how do you help a member with a balance of $2,000 on a card with a $5,000 limit keep spending responsibly? Perhaps by raising their limit to $6,000 — assuming their financial situation warrants the increase.

You should regularly review your credit card portfolio for opportunities to responsibly increase credit card limits. Your members will appreciate the extra buying power, and your board will appreciate the increased health of your portfolio.

Growing your credit card portfolio comes down to simple education and persuasion. Show your members why your card is better. Make it easier for them to transfer balances and spend with you. And encourage them to stick around with better service and financial products.