Pay your bills on time even if it’s the minimum payment – it keeps you current, you do not want a “late” payment to be reported.
Shoot for using less on each card – don’t “max out” any card. Do not close unused cards even with zero balances – shows you still have credit available.
Length of time using credit responsibly in the past shows you can manage credit or were able to at one time.
Ideally you want to have credit for different reasons, a mortgage, a car loan etc., not all for “spending”.
Each inquiry, also known as a “hard hit”, reduces your score.