There's not really anything that you can do. Don't adjust the Pot to make it more sensitive - this shortens the life. I would recommend 'no smoking' around the wii as this could potentially dirty the lens. Try to ensure that the game discs are clean before inserting them.

You can buy a new laser for around $40 and I've read that it is pretty easy to change them out. Or you could get a new DVD drive for around $100.