There are a few different reasons that can cause your TouchDesigner output to look stuttered on monitors/projectors. The obvious reason is poor frame rate, look at the Optimize article for tips on how to increase your file's frame rate. Beyond that there are a few more reasons that are a little more idiosyncratic.
30 FPS Content on 60 hz monitorsedit
While almost all projectors and monitors today run at 60 hz, you will very often be displaying 30 FPS content on them (either videos, or geometry rendering that is too heavy to run at 60 FPS). When this happens you may first want to set TouchDesigner's target rate to 30 by changing the Rate in the timeline at the bottom left to 30, to avoid needlessly trying to achieve a 60 FPS you know you can't get.
Once you are doing that you may still notice stuttering. This can occur because it's possible for some frames to be displayed for 1 refresh while others are getting displayed for 3 refreshes (on a 60 hz monitor). The best way to fix this is setting the Window COMP 'V-Sync Mode' parameter to 'FPS is Half Monitor Rate'. This ensures that each frame is shown for exactly 2 refreshes, greatly improving the smoothness of the output. One way to fix this is to use the new feature in the Nvidia Control Panel under the 'Manage 3D Settings' section. Under the 'Vertical Sync' option select 'Adaptive (Half Refresh Rate).' However that feature may introduce tearing.
The same is true for other cases such as 25Hz content on 50Hz monitors.
Windows Vista and 7 Aero issuesedit
Having Aero on can cause the desktop to randomly not display frames, even if your file is running at a perfect 60 FPS. To fix this you need to disable Aero. However this will introduce tearing on your display. To fix this refer to the Vertical Sync and Horizontal Tearing article.
Windows 8+ and Aero issuesedit
Starting with Windows 8 Aero can no longer be disabled. The only known possible solution to Aero randomly dropping frames is to ensure that the application window covers the entire desktop as a borderless window. This allows it to get exclusive access to the desktop output and can avoid Aero dropping frames. If there is extra monitor connected to the GPU that isn't used as part of the output (say for controlling the OS, or running another application) this stops TouchDesigner from gaining full control of the desktop output and Aero can still cause frame drops.