1. Roll 4d6, drop the lowest, six times and record the results in order.
2. Reroll any one result, taking the better of the two results.
3. Switch any two, and only two, results.
If your scores are too low, you may scrap them and roll all six ability scores again, without creating an NPC from them. Your scores are considered too low if the sum of your ability modifiers (before adjustments because of race) is +1 or lower, or if your highest score is 13 or lower.
In addition, if you simply do not like the ability scores, you may reroll as often as you like. However, all used ability sets must be turned in to the GM, with a short paragraph describing the ability sets as NPCs.