Never go over limit – this can expose you to huge fees. Ideally, stay below 50% (if your limit is $5,000, never carry a balance over $2,500)
Don’t close out major credit cards – sounds counterintuitive, but keep major cards open (with realistic limits – too high of a limit can keep your score down) and just use the card every so often and pay it off in full to keep your score high (no account activity doesn’t help your score).
Make sure you’re actually building credit – do you actually have a supplementary card? Could it actually be from your spouses’ or someone else’s account? Take a look at your credit card – even if it has your name and a different number, it might not be your own. How can you tell? Does the statement come in your name or your spouses’? If it’s the latter, you’re not building credit. And if you were to divorce or your spouse were to pass away, that card and the credit would be lost for good.