Stuttering or jerky playback is very often caused by the inability of your computer system and/or Premiere Pro to render and play frames as quickly as necessary for realtime playback.
Causes vary, including such factors as inadequate hard disk speed, inadequate CPU speed, and other software interfering with playback.
For information about optimizing your computer and Premiere Pro for performance, as well as finding performance bottlenecks, see this page:
"optimizing for performance: Adobe Premiere Pro and After Effects"
Stuttering or jerky playback can also occur when a sequence's settings aren't correct for the kind of footage playing in it. See this page for more information:
"FAQ: How do I choose the right sequence settings?"