I run one, which we never have to advertise because it fills up by word of mouth. So we seem to be doing something right! We do:
One painting table - either painting with brushes/fingers or printing.
One "messy" table, with trays of sand/rice/pasta/cornflour gloop or similar. Lots of spoons, plastic animals, jugs bowls etc for them to experiment with.
Two tables with a prepared craft, on a theme for the week. Normally some variation on collage, paper plate crafts, stick puppets, masks, that sort of thing.
One table with a drawing activity - sometimes just paper and crayons/pens/chalk - sometimes colouring pictures.
One table with playdough and lots of cutters.
They have free choice of what they want to do for 45 mins or so, then we have drinks and snacks, carry on playing for a bit, then start tidying up. While the adults finish tidying, I take the children through to another room for a story and some songs.
Top tips: have lots of painting aprons, wet cloths, paper towels etc. A drying rack for paintings and somewhere else to lay pictures etc (so they don't get covered in paint). Look out for activities where the children make something they can wear/play with - it extends their interest. This is a good site for ideas.
Allow plenty of time for preparation, setting up and clearing away - I spend at least 4-5 hours per week for a 90 minute session.
Locate sources of recycled materials - I get a lot of stuff from the members of the church where we meet, which keeps costs down. Ours is not commercial. We charge £2 per session and I normally have about £500 to give back to the church by the end of the year. But that's without paying for premises, staff or insurance!