I usually remove the door by folding it outwards until both points snap. I do it this way mainly because it's the quickest and easiest way. I've never had a door or frame break after doing this.
If you really want the door/frame to last as long as possible, my first obvious suggestion would be to never disassemble the the two pieces unless you have to.
A more practical solution would probably be to remove one point of the door at a time. In the example below, I removed the top piece first. Once you remove one corner the other side will disconnect without being 'clicked', it simply slides out.
You probably would want to alternate which side you remove the frame every time so that you don't wear out one side faster than the other.