You can buy a hole repair kit. If you want to avoid that and its a fairly small hole then you can easily repair it with plaster. Just re-enforce the hole with something. I like to use paint stirrers. Break them off about two inches larger than your hole. Insert them into the hole ( this is easily done by inserting a screw into the middle of your paint stirrer to act as a handle ) and then insert screws through your still intact drywall, making sure you hit your paint stirrers as well, on both sides of the stirrer. ( remove your 'handle' screw at this time ) You want to put as many stirrers in the hole as you can without causing further damage. ( ie: a light switch sized hole will take two stirrers, etc.) I usually take some kind of quick drying sealer or adhesive and glue the stirrers in place to add some integrity but this is not nesessary. If you glued your stirrers in, allow them to dry. Add a thin layer of plaster. When this layer of plaster dries clean it up a little with sand paper and add another thin layer. Keep this up until your hole is full. Don't put the plaster on thick because it will give the appearance of being dry while acutally being wet in the middle. Make sure at some late point in your repair that you remove the screws that are holding the stirrers in and go over them with your plaster as well. sand away and paint.