You will need to purchase two Joint knives commonly known as putty knives. You will need the putty knife to be at least 4 to 5 inches. There are many types of putty knives including plastic ones. Plastic is nice since it is disposable however you want a professional looking repair so use a metal putty knife. You will need to purchase a tub of joint compound and several every day sponges. If you are repairing a large area of plasterboard and not just a nail hole, you should purchase plasterboard patches. Plasterboard patches look like mesh or small screens. You can use these plasterboard patches as a way to hold the compound in place.
Remove all nails, staples, screws carefully using pliers. If your plasterboard has suffered water damage or parts are peeling off you will want to remove any pieces that are hanging. You can begin scraping with your putty knife until all the debris is removed. If your plasterboard has been damaged by water, scrape to remove all wet areas. You may come across an area that looks concave. Keep scraping until the area is flat.
Stir your joint compound until it is smooth. Take one putty knife and scoop out a large amount onto the putty knife. You will need your second putty knife to take small amounts from the other. You are ready to begin your plasterboard repair. Using small smooth strokes apply the joint compound from your putty knife onto the damaged plasterboard. After each stoke take your putty knife and scrape it on the edge of the one containing the joint compound so that you will not add any debris to the new joint compound you are about to apply to the plasterboard. Keep going with this process until you think your damaged plasterboard looks flat and smooth. While the joint compound is still wet you can reapply more joint compound to flatten out the plasterboard repair.
Lightly sponge your plasterboard repair with a damp sponge to smooth out all areas that might not be completely flat. Make sure there is no debris. You still have time to remove it and smooth it over while the joint compound is still wet. Take a step back or have someone else look at your plasterboard repair to ensure you have not missed a bubble, debris or lump. Let it dry for at least six hours. If you have repaired a large area of plasterboard it is recommended it dry for 24 hours. Now you are ready to paint.