The main factors
Common scoring models weigh your payment history, how much of your available credit you are using (utilization), the length of your credit history, the mix of account types, and recent applications for new credit.
No single change guarantees a particular result, and scores from different models can differ. Treat scores as one signal among several, not a target to game.
Accuracy comes first
Before anything else, it is worth making sure the underlying information is accurate. A report free of errors is the foundation; scores are calculated from that information.