Memorizing numbers is an entirely different story than memorizing a list of objects. The objects can easily be turned into an extremely creative imagine, but how do you turn a number into something interesting?
There is a system known as the Major System that assigns a letter to the numbers 0-9 and from this you can create an image for every number 00-99.
0 = S 5 = L
1 = T or D 6 = Sh or Ch
2 = N 7 =K or G
3 = M 8 = F or V
4 = R 9 = P or B
So for instance, the number 53 would be "LM". Your allowed to insert vowels in between the consonants, so the image for 53 could be "lime". This is done for the number range stated above and all of these 100 images are pre-memorized. The lettering system gives you a reference. That is, if you cannot remember what your lime image means then you refer back to the numbers. You can connect the images by placing them in your memory palace along a journey. Therefore, each number turns into an image that is much easier to remember and you only have to memorize half as much! (1 image = 2 numbers).
A more complex system than the Major System is the Person-Action-Object system. In this system, each number 00-99 gets a pre-memorized person action and object. For instance, one of Josh's cards was him (person) moonwalking (action) with Einstein (object). Any six digits can then easily be turned into a single image. The number 16-72-84 each has a PAO. By taking the person from the first set of numbers, the action of the second set and apply it to the object of the third, a large amount of numbers can easily be memorized.
The PAO system can easily be used to memorize a deck of cards. Each individual card gets its own PAO, for a total of 52 PAO's. Any three cards becomes a single image creating 52/3 = 17 + 1(card) images that you have to remember, instead of 52