To keep your instrument in pristine order it's a good idea to give it a regular cleaning session and probably the best material to use is something soft and fibre-free such as an old cotton t-shirt. In the same way that it's a much more pleasant experience to ride in a recently valeted car, it is actually much nicer to play a newly cleaned and polished guitar.
As well as cleaning and polishing the main body and neck of the guitar or bass, you would be well advised to get into the habit of gently running the cloth up and down the circumference of each string to get rid of dirt, debris and oils secreted by the skin. Alternatively there are products specifically designed to do this and these will generally also prolong the life of the strings.
There are many brands of guitar polish on the market, both Fender and Gibson make high quality instrument polish as do other manufacturers such as Jim Dunlop. Whichever one you choose, follow the instructions on the bottle closely and beware not to use too much as sometimes this can leave a film on the instrument that subsequently becomes sticky and attracts dust and particles in the air.
Polish the bass guitar gently but firmly to buff the wood and bring back the original lustre and shine, but being careful not to let the polish seep into areas where it may affect guitar electronics or pick-ups. The fret-board should not be treated with polish unless it is part of a Maple neck and therefore has a lacquered glaze on it. Otherwise Rosewood fret boards should be treated with a sparing amount of lemon oil to replenish the wood and restore the colour.