Step 1: Card Values
Step 2: The Count
As each card is dealt, add that card's value to the count.
For example: If an Ace, king, 2, 7,6,4, and 5 are dealt, the count is +2
The dealer's face-down card is not counted until it is flipped.
Step 3: Keep Counting
The plus-minus count is know as a "balanced" system, meaning that a standard 52 card deck will always bear a count of 0 after all 52 cards are dealt.
Step 4: Betting
A good rule of thumb is to increase your bet one increment (by $x constantly) for each count over 0.
A high count means that there are more low cards that have been dealt, increasing the probability of a high card being dealt next. The higher the probability of a high card, the higher the chance of the dealer busting and the player being dealt a favorable hand.
A low count means that there are more high cards that have been dealt, increasing the probability of a low card being dealt next. The higher the probability of a low card, the higher the chance of a dealer getting a favorable hand, and the player receiving a less favorable hand. With a very low count, however the chance of the player to be dealt "five under 21," (which is an automatic win in some casinos) in which the players hand consists of five or more cards, yet they are still not bust.
Step 5: Being Discreet
Step 6: Practice!
A good way to practice is to gather a few friends. Have one deal and monitor the count, have one or two play with you, and have one distract you. The distraction could try to talk to you, yell at you, bump into you, offer you a drink, flash lights at you, play loud music, make distracting noises or movements, or just generally be annoying.
Step 7: A Word to the Wise
This instructable is for, well, instructional purposes only. I am in no way responsible for anything you do using this information.