Hi, there are a number of ways to do this, here how I would do it:
1. Open Premiere, make new project, and import the video.
2. Put the video clip on the "video 1" timeline track.
3. Also put the video in the same position so it lines up on "video 2" timeline track.
4. Lock "video 1" timeline track.
5. Effects - Video Effects - Keying - and drag "Eight-Point Garbage matte" to the video clip on "video 2" timeline track.
6. The garbage matte lets you trace around the face with the 8 points, and it makes what ever is on the outside of the shape transparent.
7. Click the video clip you just added the garbage matte to.
8. In the monitor click effects controls - you will see the garbage matte in here.
8. Down arrow the garbage matte and in frame 1 of the clip trace the face with the 8 points.
9. Click "Toggle animation" for all 8 points. (Itís a circle/stopwatch to the left of "top left vertex" and all the other 7 points.
10. Go along the clip for few seconds until the face moves out of the circle you previously traced, and retrace it. This should make a key frame for each point so that it animates, meaning each frame it will automatically move the circle you traced close to where the head moves, if you want it to be dead arcuate, you can trace the face in every frame, but you donít need to.
11. Once you have gone through the clip and the face has been traced throughout. Itís time to add a blur.
12. Effects - Blur & Sharpen - drag "Gaussian Blur" to the clip where the garbage matte is.
13. Under effect controls for that clip, (where you set the points for the garbage matte) down arrow Gaussian blur and set blurriness to 10 or what ever you need to blur the face.