At times you may need to get the most possible warmth you can out of your electric space heater. Whether stretching a small heater to heat a room larger than its intended for, or whether trying to warm a room that feels as though its made of ice, these tips should help you get as much as you can out of your heater.
First, keep the room enclosed. If you're heating a room with doors and windows, keep the windows closed and the doors shut as often as possible. Leaving even a crack open could let out some of the warmth of the room. You can also shut out extra cold from windows by laying heavy curtains across them, laying thick blinds in front of them, or placing thermal wrapping against the windows.
If you have a much larger room that you're trying to warm, you could try having 2 separate heaters running in opposite sides of the room. The combined effort of even 2 small space heaters could warm the room much better than you'd think. Try not to place them right against opposing walls, but rather halfway between the center of the room and their respective walls to get the most warmth for the room.
You can also try doing the above tip for a larger room with 1 heater, if you need to. It takes a little bit more work, of course, and it may not work quite as well as with 2, but it should do. See, many heaters have a point where they turn off for a bit when the area around them is heated to the proper temperature. When you see this happen you merely move the heater to the other side of the room and set it to warming that area up. Once its done, it goes back to the other side again; back and forth. As I said, its a bit more work, but it should do in a pinch.