Sandra,
As you know, I use Powergrip straps too. My tip for you in this instance is this- From a stop at an intersection, when I am ready to go, I put ONE foot in my strap and push off on that foot and I just put my other foot any old way on the other pedal and get going. Once I am PAST the intersection and UP TO SPEED, I then flip the other pedal over and put my second foot in the strap. I don't put my second foot in the straps until I am cruising along with no more interference.
Also. I don't take both feet out of the straps when I stop. I take out the foot that's going to step down on the ground and I then lift off the saddle and forward onto that foot that's planting on the ground, while braking, all in one motion. That way, there is no way I am caught still in the saddle and able to tip over when I am stopped. By the time I am stopping I am already forward off the saddle with my foot coming down onto the ground.