Some guidelines that I give myself when I name characters:
#1. Either make it up or pick rarely used one. As you mentioned already, I'd eschew the more common names of John and Sarah unless for some reason you mean to point out their normalness. In a script that I wrote recently, I used entirely made up names, such as Nonry and Henren because I wanted my characters to appear normal. However, in a film script I wrote a while back I used the names Jay and Mike because I wanted these characters to appear as more normal.
#2. Name characters with different sounding names or at least different initial letters. So please never do: Joshua, Jonathan, Samantha, Sam, Susan. Unless you're using it to associate characters together.
In a skit I recently wrote (and yes, it has been performed), I used Mario, Luigi, Linguini; Katya, Igor, Misha; Sparks, Chips, Dipp; Charlie, Dr. Flynn, Dr. Ford. I realize that I broke my own rule a little but, but I wanted people to associate Flynn and Ford together, and I wanted to use some humor with Luigi and Linguini.
On the more serious game side, I used the names recently: Salato, Rikas, Manx, Armus, and Lorian. Just to name a few of the characters, but each of these names has a different sound and initial letter.
#3. Name characters as they should sound based on their natures. Darth Vader sounds much more sinister than Fath Mithor. This is because the harsh sound of
dar- sounds menacing, and the trailing of the
-er sounds like a growl. However, we get a sense of nobility from the sound and
vad- because of the latinate sound of it. I realize some of you might think I'm over thinking this, but these are standard practices in poetry writing. Below is a classic example:
Many-maned scud-thumper, tub of male whales,
maker of worn wood, shrub-ruster, sky-mocker, rave!
portly pusher of waves, wind-slave.
#4. Pick names appropriate to the world. If you're writing a sci-fi or fantasy, by all means, make up the names, but if you're writing for a modern or historically set game, don't go all crazy and bring in Private Samothil Brorogard of the 101st Airborne Division.
On a different note, I've actually a couple of times set up naming conventions if I really want to build a world around some characters. Below is an example of what I've done before:
Gumark
Strong use of B, G, K, R, T, V, W. Tendency toward short vowels. Often combines several consonants together.
Formula
Given name + Father Name + Family Name
Baldric Votakotor Bok, Baroggae Tormin Gowvorar
Male names
End in –ar, -ot, or –in.
Baldric, Detmar, Vokrar, Draggot, Morlin
Female names
End in –ae or ee.
Broggae, Driaree, Rablae
I actually would strongly advise using naming conventions if you're looking to make a large, immersive world. Having a strong sense of where culture is often driven by the naming conventions of a society. So in the game that I got the example above from, I used 4 different naming conventions to set off the different cultures that the player would engage in the game.
So that's my twenty-three cents. What about the rest of you guys? Ever make rules for yourself like these or set up naming conventions?