Before you begin to do anything, have the bassist walk around the room to find the "sweet spot" in the room. This is the spot where he feels best playing the instrument, and also where the instrument sounds best. Unlike an amplified instrument, the upright bass is acoustic and the player is intimately aware of his instrument and where it will sound best. Trust him in this regard.
Once you've found the "sweet spot" you can begin to set up. One thing to consider is, that contrary to popular belief, the sound is not always best coming through the "F-hole" on the bass. In fact, it is similar to a port on a subwoofer. Think of it as sort of an exhaust system. It allows the low frequency buildup to escape from the instrument.
I generally prefer a three input setup for this instrument. One ribbon or condenser microphone for the detail and nuance. One dynamic mic for a more direct and focused sound. And one D.I., usually installed as a pickup on the bass.
If you are looking for a good bluegrass or traditional country thump, place a Shure SM57 and wrap it in a small towel or perhaps a sock. Wedge it sideways under the strings between the tailpiece and the bridge. When augmented with a condenser microphone the results are quite useful. This works for many applications that require a dead, thumpy bass sound. Great for RnB.
My usual setup incorporates a ribbon microphone placed approximately 9 to 12 inches from the nut at the top of the neck. I place another dynamic mic such as a Shure SM7 or an AKG D112 at the bridge. I then add the D.I. and blend accordingly. This covers a wide range of musical styles. My reason for micing in this way is that I like to capture the sound of the nodes. These nodes are at the bridge and the nut of the bass. Perhaps a bit unconventional, but it works very well.