After you encrypt your wallet the most important thing you should do first is making a backup of your wallet.dat file.

Whenever you make a new receiving address you should back up your wallet. The simple reason for this it's for security and the possibility to avoid depending on a PC that could one day stop functioning.

After you select the option to back up your wallet you should name your file and choose a location where to store it. You can choose your own machine, USB or an external drive that can store it as well. In this way in case your machine hard drive gets corrupted you can always import it to another machine and get use of your funds.