If it's plain wireless, make sure there are no other wireless input devices in range. Bluetooth? Make sure your Bluetooth adapter isn't being used other than for your input devices. Wired? Check the connections.

For laser mouses, make sure the lens are clean of dust, and other particles. For Optical, the same, make sure the lens are clean, for both laser and optical, make sure that the surface is smooth, and clean.

For ball mouses,make sure you clean the ball, and the track wheels.

If nothing above helps, double check that your input devices are not faulty, by checking them on different computers, or try another set on your computer, if possible.

-------
A positive attitude can make even the hardest of jobs easier! :D