What you did isn't really AA, all you did was outline everything with a lighting color. But what you got is going to be very hard to AA because of the awkward lines...
When you're doing lines in pixel art, it's a good idea to keep it at a ratio. IE, for every 1 pixel you move up or down, move 2 pixels left or right. For every 1 pixel you move left or right, move 3 pixels up or down. Right now, like on the gun barrel, you're going 2 pixels to the right, then 2 pixels diagonally, then another to pixels to the right, it makes for very choppy lineart.