The thing about riding clipless is that you have to focus and always do it exactly the same way. You have to be somewhat compulsive in the beginning to always clip in/clip out, start/stop the same so that it becomes like breathing...
I have found that unclipping left foot first works best for me. You can unclip it in advance of the stop. Try to unclip and just let your left leg hang down a little in front of the pedal, you are braking/coasting to the spot where you want to stop. Right foot is still clipped in and most likely in the down pedal position. When you are ready to stop, fully engage the brake and just put your left foot down to complete stop. Obviously, you have to leave the saddle to get your left foot all the way down on the road. Leave your right foot clipped if you are just stopping for a stop sign or some obstacle. Make sure to keep your brake engaged so you don't roll off with your right foot clipped... you are a one legged girl on a skateboard at that point! Bike is leaning a little to the left.
When you're ready to go, just lift your right foot to about 2 o'clock position, push off on your right and hoist yourself back into the saddle. Now you're rolling and can clip in your left foot again. I have found that I sometimes have to make one or two pedal strokes to get my darn left foot re-clipped. That's ok, cause your right foot can make slow revolutions while you get the left foot clipped again.
If you repeat this over an over an always do it exactly the same, eventually it becomes a habit and clipping in/out is natural.
You can do this fast as well, if you don't know in advance that you have to stop, you can quickly unclip left, apply full brake, hop down from saddle and plant your left foot leaving right foot clipped in.
I have seen people unclipping on the right and even unclipping both feet at once and hopping down and it looks incredibly difficult to me... maybe because I am now brainwashed to unclip on the left. Also, on the trainer or spinning bike, it's opposite for me, unclip on the right.. but I'm used to that as well.