If you make any changes to the figure's pose, you have to do them all in the same frame. As AmbientShade stated, you load your zeroed out model at frame 1. I usually pose the figure at frame 15, giving me 15 frames for the cloth to settle on the figure. If you do make changes to the figure or the cloth, do it at the frame you did the pose in. And before you begin a simulation where you made changes to anything, there is a button on the bottom right that says 'Clear Simulation'. Click that before you run the simulation again.

If I had a nickle for ever time a woman told me to get lost, I could buy Manhattan.