Step 1: Rules
In every nerf war their are rules. You should sort them out with all participants before starting. This is a basic guide of the rules and modes.
Step 2: Game Mode
What type of nerf war are you playing? Death match? Team death match? Capture the flag? Humans vs zombies? Think carefully about these types and decide what bests suits your group. For example; you wouldn't play humans vs zombies with two people. Maybe you could play death match instead.
Step 3: Weapon Restrictions
What type of weapons are you allowed to use? Nerf brand only? Single shot only? Anything goes? Think about this as well.
Step 4: Death Rules
When you get shot are you out for the count? Do you wait 10 seconds before you respawn? Do you join the other team?
Step 5: That's It!
That's all the basic nerf rules. Have fun!