Anki cards. In my opinion, this is the best way to retain new information. If you want to pass the CCNA exam and get your certification, you will have to learn a lot of new commands. This is where Anki comes in. Everytime you come across something new that you need to remember for the exam, simply write in down on an Anki cards.
The algorithm in the software takes care of the rest. Every morning, on my way to work, I take five minutes to do my Anki cards.
Share your own cards in the comments below.