Kill an enemy +2 points
Change an enemy flag to neutral +2 points
Convert a neutral flag to your side +2 points
Flag assist +1 point (note 1)
Kill assist +1 point (note 2)
Flag defend +1 point (note 3)
Driver assist +1 point (note 4)
Heal 100 points of damage (other players only) +1 point
Revive a player +1 point
Give ammunition to player or vehicle (other players only) +1 point
Repair a vehicle +1 point
Team damage (take off 50% of a teammate's total health) -2 points
Team vehicle damage (deal 50% damage to a vehicle controlled by a friendly player) -2 points
Team kill -4 points (note 5)

Note 5: DiCE seems pretty serious about penalizing players for going after their teammates. You get a two-point penalty for dealing 50% damage to a teammate, then another four points for actually killing them, so you'll earn an eight-point penalty for killing a perfectly healthy teammate. (This is what it theoretically should be, but in most cases you wind up getting -6; apparently everyone takes a small amount of damage while spawning. You only get the minimum -4 points, however, for killing a teammate instantly, such as with a shotgun blast to the head or by running them over with a vehicle.) These penalties apply to teammates in vehicles, as well, so if you "accidentally" blow up a fully-loaded APC or helicopter, you can expect to take some massive penalties. What's more, server operators can set their servers to automatically kick players when they earn a set number of negative points, so you'll want to check your targets on servers with friendly fire turned on, which we expect will be almost every ranked server out there.