Wet your razor handle and apply a small amount of soap to the handle to get it slick. Wet the inside of the grip sleeve.
Wrap a towel around the sleeve so that you can get a good grip on it. Position the small end of the grip at the bottom of the razor handle and push it on. Wrap a cloth around the wet grip to make pulling it up easier. Bring it to the bottom of the "Y" at the peak of the handle.
Once positioned, rinse the soap-assist clean. Run water through the grip sleeve on the handle, inside the top, through the bottom, and through the sides. Keep rinsing until you feel the grip holding the handle instead of sliding around. Let it dry a bit, the sleeve should be firmly grabbing the handle now.