Maybe you have watched a few episodes of Sherlock and see him use his "memory palace" to fight crime and are thinking to yourself "hey, I wish I could do that!" The good news is that Sherlock's memory palace technique is not science fiction or fantasy. It is an ancient technique that uses your ability to remember places in vivid detail to remember abstract things like sequences of numbers or words. A great way of getting your feet wet with this type of mnemonics is to learn how to memorize a deck of tarot cards.
No, I'm not advocating witchcraft (at least not here.) To explain why tarot cards are great for learning mnemonics, I will have to explain a little bit about both.
One of the oldest mnemonic devices used today is the the method of loci, a technique that dates back to Ancient Greece and Rome. It was used by public speakers and scholars for centuries but waned in popularity with the dawn of the mass-printed word. To sum up how the method of loci works: users create "mind palaces" in which they place people or objects that represent other things (such as words, concepts, letters, numbers, etc...) The user also creates a set path in which they travel each palace - called "the journey" - so when a user wants to do something like remember a sequence of numbers they go along their set journey in their memory palace and place people or objects which they have chosen to represent the numbers and "place them" in prepicked spots on their journey called "loci".
Standard tarot card decks come with two sets of cards: the Minor and Major Arcana. The Minor Arcana look more or less like a standard card deck except the suits are things like cups and swords. The Major Arcana is the set we will use. It is comprised of 22 cards that are represented by characters akin to Jungian archetype. These characters are things like The World, The Fool, the High Priestess, etc... and will provide you with easy symbols with which to populate your memory palace.
Before you can use your first memory palace you will have to do three things: pick a memory palace, create your journey and create symbols. It may be beneficial at the beginner stage to write these things down but you will soon see that remembering these things comes almost naturally.
For your first memory palace, it is a good idea to pick a place you are intimately familiar with that is fairly large. A place like your school, the office, or a favorite park would be ideal. Take some time to imagine the place as accurately as you can. Remember things like prominent structures, how many rooms there are, where the rooms are, and how those rooms are furnished. The more you can remember the better.
Go through the rooms in your first palace and start looking for places to use as your loci - where you store the symbols which represent the cards you are trying to remember. Pick places that are fairly obvious and make for a "smooth" journey. If you are using your high school, for example, try and pick a journey that you are most familiar with in that building. Start at the front office and then go along a path you would have used frequently like your morning walk to your locker. Create loci on this path out of things like the doorway to the school, the front office, the classrooms along the path, that art installation near the auditorium and so on. Take a few dry runs of this journey to "set it" in your mind so you will know where to place your symbols.
The archetypal characters used in the tarot card's Major Arcana are numbered and go from 0 (the Fool) to 21(the World). To create symbols for these cards simply choose characters that you would recognize instantly. These characters can be from film, television, pop culture, novels or people and things in your day-to-day life. It may help to use characters all from the same universe. You could use, say, the Harry Potter universe and use Snape, Dumbledore and Bellatrix to represent the Fool, the Magician, and the Empress (respectively.) For the non-human Arcana cards like the World or Judgement I would recommend using people to represent them. It would be a good idea to write down these associations as a beginner.
At this point you are ready to take your first journey in your palace. Shuffle up your deck of 22 Major Arcana cards and lay the deck face down. Draw the first card and then go to your first loci in your mind. Spend a few seconds remembering the character in this spot - how he or she is standing, sitting. You may want to have an interaction with this character by having a quick conversation or have them say any catch phrase they may have. When you feel you've looked at the loci long enough, place the card face up in front of you. Imagine yourself walking to the next loci, draw the next card, and repeat the process until you are at your last loci. Make sure to stack the cards neatly so they maintain the order you drew them.
When you've gone through the deck turn the whole deck over. Go to the start of your memory palace and look at your first loci. There you will see the character you had put there. Say out loud which card he represents and turn the first card over - it should be the card you just named. Repeat this process with every loci on your journey. If you want to track how many cards you get right, lay the cards you get right in one deck face down and the cards you get wrong face up (which deck is face up or face down is up to you, but keeping them different will help you remember which is which.)
When I did this the first time, I got 19 out of the 22 cards correct. Within a day I was able to run through the whole Major Arcana and get them all right. The tarot cards I used was this Vertigo tarot card deck, which I had gotten because I'm a massive Hellblazer fan. Once I had a good hold on this I went on to learn how to memorize a standard playing card deck.
If you want to find out how to use memory palaces for more practical purposes, check out the Mnemotechnics forum to see discussions on using the method of loci to do things like study for tests or learning languages. They also have a wiki where you can learn about the foundations of modern mnemonics like the major system and the PAO system. Soon you will be able to remember complex things like important vocabulary for that language you are looking or all the important concepts you need to pass your next final.