Several ideas stated and they are all close.
Credit cards best utilized at different tiers; cards under 30% of limit best, under 50 good, under 70 meh, over 90%derogatory and over your limit obviously worse. Credit reported to the bureaus the highest limit from previous month so if paying off once a month and running over 90% of limit bad. If you have the credit history like some have here no problem, but if you have no history or limited then it will be weighted more and can hurt you quicker. Variety of credit best such as revolving credit, installment, etc.
There are over 52 algorithms to determine scores and each one differes based on type of credit applied for and if it is a hard pull or soft pull etc. This is just a basic statement from typing from my phone but it is a complicated issue but rhe sooner you lear n the better or it will cost you later. For instance, it is true to not close out cards without fees however use them once a month for 10 bucks and pay it off. A hibernated tradeline will not do much as said tradeline will not pay the bureau's to report unless there is activity.
#not preaching