I'm brand new to clipless too.

Yesterday was my second attempt. I had tried in the parking lot a couple weeks ago and promptly fell over and scraped my knee. I wasn't hurt really, but it was the mental panic that got me. I couldn't get over the moment of panic when I realized I wanted to stop and was "stuck." Sounds like you might not have that, which is awesome.

When I went out yesterday, I first loosened the SPD clips a TON. I think what caused my fall last time was that the clip on my right was too tight and I went for my left (not the usual) foot and then leaned right and fell over.

This time, with the clips really loose, it was so much better. I rode for a long time without stopping, initially with my feet not clipped in, then clipping and unclipping repeadtedly, one foot and then the other. It gave me a good feel for it and started breaking down the terror at being trapped that I was having so much trouble with.

Finally, I clipped in and then practiced stopping along a small stretch. The routine, as others have said, does seem to be the key. Once I had that without breaking into cold terror sweats and tears, my boyfriend would ride in front of me to anticipate potential hazards and would randomly slow and stop in front of me to force me to learn how to do it when I wasn't expecting to.

It really helped to do it this way. I had a few moments of just thinking I would never get over the fear and was ready to pack it in. I don't know how tight your clips are, but it might help to loosen them so it takes almost nothing to get your foot out. It really screwed me up having to think about rotating my foot with so much pressure when trying to stop. I also found that when I did only small stretches of start, then stop, I was worse at it. It really helped to pedal awhile straight before stopping instead of just a short distance.

Keep at it!