The following method will give you approximately 49.5% odds versus the House in a casino. Over the long term, of course: over a few hands you could win or lose big, that's why it's called gambling. Since most players have no idea what they are doing, using this method will let you crush your (soon to be former) friends. Remember, your milage may vary, especially if you aren't so good at memorization. The first step is to learn the rules of Blackjack, then memorizing the tables. I'd suggest learning with some friends: rent the movie Croupier, sit around alternating playing the dealer, and make sure it works for you before going into a casino and losing big. One more point: the odds are for winning or losing, if you vary your bets from hand to hand, you'll mess with your bottom line. The easiest way to go is to bet the same amount each hand.

This method is often called "Basic Strategy", since it (or a similar set of tables) is the basis for almost any feasable scheme to beat the house. Combining these tables with various ways of counting cards can push your odds over the break-even line. It is sometimes called "playing by the book", and a kindly croupier will sometimes say "the book says to do this," if you are looking like a perplexed beginner.

This set of tables builds on the same idea as the method noded above: the hard totals table below is quite similar to the table given above. Among other things, the addition of the soft totals table tells you to hit on any soft seventeen (an ace and a six), and double down, if the dealer shows a 3 thru a 6. The tables are optimized for when the House playes with six decks, the dealer hits on soft seventeen, you may double after you split, and you are allowed late surrender. The tables also show what you should do if you're playing somewhere where doubling down and/or surrender isn't allowed. "Late surrender" means you are allowed to surrender after seeing your hand. Most casinos offer this, but you'll need to ask beforehand. Always ask.

Key to the tables

There are three tables. Refer to splitting pairs when both of your cards have the same value. Refer to soft totals if one of your cards is an ace. Otherwise, refer to the hard totals table. Look down the first column for the row that matches your hand, then follow across to the column matiching the value of the dealer's showing card. The code in that cell will tell you what to do. You'll want to copy the tables into something which will let you change the font to something wider like Terminal or Lucida Console.
         Ten - a 10, Jack, Queen, or King.
          Y  - Split (then apply tables to each resulting hand)
          ×  - Don't Split (use hard or soft table instead)
          S  - Stand
          H  - Hit
          D  - Double Down
          R  - Surrender ("Resign")
         X/Y - Do X if possible, otherwise do Y.


.-----------------------------------------------.
|                                               |
| Splitting Pairs, or To split or not to split? |
|                                               |
>-------v---------------------------------------<
|Your   |   D  e  a  l  e  r    S  h  o  w  s   |
|  Pair |                                       |
|    Is…| 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |Ten|Ace| 
>-------+---+---+---+---+---+---+---+---+---+---<
| Aces  | Y | Y | Y | Y | Y | Y | Y | Y | Y | Y | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Tens  | × | × | × | × | × | × | × | × | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Nines | Y | Y | Y | Y | Y | × | Y | Y | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Eights| Y | Y | Y | Y | Y | Y | Y | Y | Y |R/Y| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Sevens| Y | Y | Y | Y | Y | Y | × | × | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Sixes | Y | Y | Y | Y | Y | × | × | × | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Fives | × | × | × | × | × | × | × | × | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Fours | × | × | × | Y | Y | × | × | × | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Threes| Y | Y | Y | Y | Y | Y | × | × | × | × | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
| Twos  | Y | Y | Y | Y | Y | Y | × | × | × | × | 
`- - - -^---^---^---^---^---^---^---^---^---^---'


.-----------------------------------------------.
|                                               |
| S o f t   T o t a l s  (When you have an ace) |
|                                               |
>-------v---------------------------------------<
|Your   |   D  e  a  l  e  r    S  h  o  w  s   |
| Other |                                       |
|   Card| 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |Ten|Ace| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  Ten  |   B   l   a   c   k   j   a   c   k   |
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   9   | S | S | S | S | S | S | S | S | S | S | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   8   | S | S | S | S |D/S| S | S | S | S | S | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   7   |D/S|D/S|D/S|D/S|D/S| S | S | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   6   | H |D/H|D/H|D/H|D/H| H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   5   | H | H |D/H|D/H|D/H| H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   4   | H | H |D/H|D/H|D/H| H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   3   | H | H | H |D/H|D/H| H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   2   | H | H | H |D/H|D/H| H | H | H | H | H | 
`- - - -^---^---^---^---^---^---^---^---^---^---'



.-----------------------------------------------.
|                                               |
|   H a r d     T o t a l s    (Anything else)  |
|                                               |
>-------v---------------------------------------<
|Your   |   D  e  a  l  e  r    S  h  o  w  s   |
|       |                                       |
|  Total| 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |Ten|Ace| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 7  | S | S | S | S | S | S | S | S | S |R/S| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 6  | S | S | S | S | S | H | H |R/H|R/H|R/H| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 5  | S | S | S | S | S | H | H | H |R/H|R/H| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 4  | S | S | S | S | S | H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 3  | S | S | S | S | S | H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 2  | H | H | S | S | S | H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 1  |D/H|D/H|D/H|D/H|D/H|D/H|D/H|D/H|D/H|D/H| 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  1 0  |D/H|D/H|D/H|D/H|D/H|D/H|D/H|D/H| H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|   9   | H |D/H|D/H|D/H|D/H| H | H | H | H | H | 
>- - - -+---+---+---+---+---+---+---+---+---+---<
|  <=8  | H | H | H | H | H | H | H | H | H | H | 
`- - - -^---^---^---^---^---^---^---^---^---^---'

(The exact percentage of the odds is to the best of my recollection: someone is welcome to back me up or correct me on the exact odds.)