If you're building credit from scratch, it's better to start with a secured credit card. A secured credit card is backed by a cash deposit you make upfront.
Use your cards to make frequent small payments as credit utilization is a big factor in your credit score. However, it is advisable to keep your credit utilization below 30% on all of your cards.
Late payments could reflect on your credit history for seven years! Prevent that from happening by paying on time, every time.
You might think that closing your financial account will help boost your credit score. But that is not the case. As long as they are not costing you annual fees, keep unused accounts open. Closing your account could increase your credit utilization ratio, thus lowering your credit score.