If it is a music/singers club
1) start at the appointed hour every time, if there are only a few people in - be the brave one - start. Or people will poke their heads in, hear nothing and assume nothing happens - believe me.
2) smile
3) include everyone, those that don't sing/play talk to them in the break. Particularly new faces.
4) make sure there is someone to run the nights that you can't be there and tell them rule 1 - 4.
5) make it clear if you only run during term time etc.

If you are paying guest performers - there is a lot more to it and the same rules above will get you started. But contact with the guest during the week before to check all is as you expected would save any embarrassment and give you time to deal with eventualities/uncertainties like arrival time and picking-up from the station or navigation instructions etc.

Oh and use your free publicity channels, like posters, students union (flyers work - hand them out personally) , local radio, newspapers, TIC and any websites like mine I may have a link to your area (certainly Scotland).

And come back here and tell us how it is going.