House rules and variations for both play and scoring need to be discussed and agreed upon before play starts.

The object of the game is to be the player with the highest score over 10,000 points.

To start game play the first player is decided by each player rolling one die the player with the highest value starts. If two or more players tie, the youngest player starts first.

Players take turns rolling the dice. To begin a turn, a player rolls all six dice at once. Points are earned for various scoring combinations. If no points are scored during that roll, that's called a "Farkle" and you lose your turn, and score no points.

If any points are scored during that roll, you have the option of either banking the points, and relinquishing your turn, or pressing your luck and rolling again, using the dice that were not scored during the preceding roll(s). You can keep rolling, and keep racking up points, until you either bank your points, or roll a Farkle and lose all the points from that round. If you manage to score all six dice (whether in one roll or multiple rolls), start the next roll with all six dice again. To get on the board for the first time, you must score at least 500 points on a single turn. (In other words, your first bank must be at least 500 points.) After that, you may bank as many or as few points as you like during a turn.

The Game ends with the first player reaching a score of 10,000 points, each player has one last turn to try and come out on top. The player with the highest score at the end of that last round wins the game!
Here are the points awarded to various rolls:
Single "1", 100
Single "5", 50
Three 1's, 300
Three 2's, 200
Three 3's, 300
Three 4's, 400
Three 5's, 500
Three 6's, 600
Four of a Kind, 1000
Five of a Kind, 2000
Six of a Kind, 3000
Straight (1-2-3-4-5-6), 1500
Three Pairs, 1500
Four of one number, Pair of another number, 1500
Two Triplets, 1500

Adapted from http://www.boardgamecentral.com/rules/farkle-rules.html