For stuff like decks of cards and long numbers this is very difficult and requires practice. But there are easy examples you can do to show you the power of this method. For example, I tried memorizing the basic layout of the electromagnetic spectrum about two years ago. This was accomplished in about five minutes and I can still recall everything with clarity at this very moment.
For numbers, I've partly described the "peg" system in a comment above where you assign sounds to the numbers 0 to 9, then make words that reflect the number sequence with the matching sounds, using vowels to fill in.
For cards, it's a similar approach: For example, for the diamonds suit you begin each member with the letter d and join it with the appropriate number ( 2 : n, 3 : m etc) so that two of diamonds becomes DeN, the three of diamonds DaM etc. Using this kind of mnemonic to represent the cards it becomes very easy to visualize and remember them.
I've done this and astounded people by calling out the order of a deck of cards in sequence - forwards and backwards, the card in any random position in the deck, and the position of any random card. A lot of fun, and a lot more useful in practical applications that call for a good memory.