Raising credit score

I have about 3,000 in debt that I plan to pay off before June 2019. Maybe even before.

My score is mid to high 600s. Just wondering if there are any other tips to help me raise it? I have 4 credit cards and only 2 are nearly maxed. After I’m done paying them off I plan to only charge 1 bill on them every now and then to keep them going. Any tips?