When you choose a password for your user account, it's important to pick something you can remember. You're going to need it again later! To help you remember your password, you can add a password hint, as long as your PC isn't on a domain. For detailed steps, see Create or change a password hint.
Of course, you can also write your password down and keep it in a safe place. Taped to the underside of your laptop or the inside of your desk drawer is probably not a good idea, however. If you do write your password down, be sure to keep it separate from your PC.
For added security, consider using different passwords for different purposes. For example, you might want to keep one password for all your social networking accounts, and another one to sign in to your online bank account or other financial services.
If you do forget or lose your password, there are still several things you can try to reset or recover it. For more info, see What to do if you forget your Windows password.