Adjust the tension as loose as can be ridden safely without inadvertently unclipping while mashing on the pedals or tweaking your leg to adjust your position on the saddle. After switching from toe clips I've only had one close call, which was mashing uphill when a car pushed me into a pothole at less than 5mph while creeping to a 4-way stop.

It also helps to use two sided pedals (cleats go in one side, flats on the other); using these, you can anticipate a bad situation and unclip ahead of time. If the situation warrants unclipping, you can then just bail as you will, at that point, already have been on the flats. It also helps to learn to balance your bike while at a near stop and still clipped in, e.g. creeping behind a car at a multi-way stop or waiting for a light to turn green.