Before closing any accounts, you need to think carefully about what you may need credit for soon. If you have several accounts open and are not using any of them, closing some could help improve your rating with potential lenders but there is an argument to keeping at least one card still open.
Lenders like seeing a long history with the same lender so it could benefit you more to keep your oldest card active.
If all your cards are still being used however, it may do more damage transferring all your credit onto one card and closing the rest. This is because lenders will see that you have one card with a lot of credit being used which makes it look less manageable. Splitting your credit across multiple cards could cost more long term depending on any offers you have and the individual interest rates, however lenders look more favourably at cards where only 25% of the credit is used.