A medium rare steak should be warm through the middle with a hint of red. Most of the center of the steak should be pink. The sides should be well browned, the top and bottom charred to a dark brown color. This steak should have a firm surface but soft in the middle.
Grill this steak as hot as you can for about 2 to 3 minutes per side (depending on your grill).
This is the recommended level of doneness for a good steak. Ask any chef how they like their steak prepared and they will, say medium rare.