Is any of your artwork a candidate for display as a grouping? Photos/paintings of a similar size, theme or color scheme, sculptural pieces that complement one another (see my three "Personal Muses" displayed together at right), pottery that could make up a set, etc. If so, you've got an oppurtunity to sell multiple pieces.
When you setup your work for display and sale, arrange pieces so that items that work together are displayed together.
Take this a step further and consider your pricing structure. Price each piece separately and as a grouping (I like to give a small discount - something like $100 each or 3 for $275 ).
This tactic works several ways - many will buy the whole grouping; others may get idea of group display in their head and become return customers, building up their collection over time.