General usage ideas and techniques for NPCs. How much is to much? Do you have too many NPCs orbiting the party? Is the one NPC overshadowing or outshining the party? Discussions on what to do and NOT to do with an NPC.
Never outshine the player with an NPC. I've found that gets the NPC killed if the players are angry enough. The point of the game to focus on the players and if you can avoid having an NPC tag along with the players, do so. They're fine every now and again but they're a big distraction. I've never been able to grow out of forgetting that the NPC is there.
Do: Drop a plot hook, assist on a short-term basis, sell the PC's short, sell the PC's out, make them a reoccurring face or villain.
Don't: Give the NPC a bigger spot light, make the NPC's story more important than a 'main' plot hook, give the characters too much in the way of help, forget the name of the NPC.
I give my NPC's have a specific ability or set skills and an area they patrol. I use them to help direct the players if they are to far off the course and as a reminder of do you really want to ditch the current adventure? I some times have a minor NPC to tag along for a short time and leave the party or they die in combat. I never have them out shine the party nor do i have them completely bail the party out. It can be a good way to interject comedy into the game as well.