Check out the 'xset' man pages:
m The m option controls the mouse parameters. The parameters for the mouse are ‘acceleration’ and ‘threshold’. The acceleration can be specified as an integer, or as a simple fraction. The mouse, or whatever pointer the machine is connected to, will go ‘acceleration’ times as fast when it travels more than ‘thresh-old’ pixels in a short time. This way, the mouse can be used for precise alignment when it is moved slowly, yet it can be set to travel across the screen in a flick of the wrist when desired. One or both parameters for the m option can be omit-ted, but if only one is given, it will be interpreted as the acceleration. If no parameters or the flag ’default’ is used, the system defaults will be set.
You may have to just try out different parameters to see what you like.