Why is my mouse pointer twitching?

Whenever a mouse doesn’t work correctly and the pointer skips or jumps, the first thing you should do is to clean it. The rollers on ball mice accumulate dirt and oil and need to be cleaned, but even optical mice need to be cleaned, especially ones that are particularly sensitive and have high resolutions.

Check both the optical sensor and light closely for hair, particularly if you have a pet with very fine hair. These are small an light enough to remain stuck in there, unnoticed for quite a while, but are still visible to the optical sensor. This is a common cause of phantom optical mouse movements.

One way to prevent this is to place a small strip of clear, Scotch tape over the area.

Sometimes I'll see "phantom" mouse movemement with optical mice (perhaps the pointer is travelling slowly even if it's not being touched, or the pointer motion is jerky in general) if the mouse is sitting on a surface with certain reflective properties, or if the surface is dusty.

An optical mouse uses the reflection of light off of your desk to track the motion of the mouse. If the surface of your desk has particles causing the light to reflect in odd ways, or if it is a very reflective surface, it will not be able to get a clear idea of its motion. Think of looking across a very clean window or mirror and trying to see the glass itself travel across your line of sight. It's the same problem.

Basically, the solution is to find something to put down on the under the mouse (like a piece of printer paper), or get a mousepad (they still are useful for this purpose). Or simply wipe any dust off your desk, and make sure there isn't a buildup of dust under the mouse itself, near the lens.