securely stored 1 or more good backups of the wallet
don't forget to backup your old wallet
have a backup ready.
Make sure you backup.
Hopefully by now you've caught on to the most important step.
It's a shame it has to be said so often. Even so, there are still people that come to this forum almost every day and ask for help getting their bitcoins back after they did something they didn't understand and didn't have a backup. Unfortunately, there frequently isn't anything than can be done to help by then.