I started at 10 incline and 2mph walk for 20 minutes. Now I'm working my way up to 5-6mph fluctuated. It was by accident since I didn't realized it was inclined for the longest time, but now I'm glad as my endurance at 1 incline running is a breeze.
I highly recommend treadmill trainer is Amy Dixon,he has a coached workout album called 'Treadmill Coach' that's completely audio based .I need for an effective workout. And the workout is interval-based so it helps me burn calories faster.