I don't think there is a trick to this, other than being patient and discerning. I think the issue is that it is hard to be patient and discerning, especially in the face of that closed door. Opportunities have a way of presenting themselves if we will recognize them, and a way of slipping through our fingers when we are trying to force things.
This difficulty is, I suspect, because we like to be in charge, in control. We like to plan ahead and cause things to turn out the way we want them to. We set up the whole scenario in our minds, including the part where others go along/acquiesce/act the way we want them to. And then we're frustrated when things don't turn out the way we planned or envisioned them. And we don't necessarily like surprises, either, when we are in "I am planning my life now" mode.
This is where one remembers the saying, "If you want to make God laugh, tell her your plans."
I don't know if its some kind of cosmic-waves-conveying-our-needs kind of thing or just prayer and patience, but I can think of a couple of stories from Anne Lamott that illustrate this. One was the time her car died in traffic. And she was already at the end of her rope. And so she just prayed one of what she calls her "two best prayers" - "Help Me, Help Me, Help Me." (The other best prayer is "Thank You, Thank You, Thank You.") And in a few minutes, someone came along, a friend of hers, and there was her help. Another time she won a ham at the grocery store, and she doesn't eat ham and didn't want the ham, but she figured if God wanted her to have this ham she should take it, and as she was wheeling it out to her car, another friend came along who was in sad and dire straights, out of money and hungry, and she gratefully gave the ham to her and her friend gratefully received it. You'd have to read the stories straight from Lamott's books (Traveling Mercies, and Plan B) to get the goodie out of them, but those of you how know her work will probably remember them.
These aren't exactly examples of windows and doors, but they are examples of patience and discernment. Sometimes things happen a certain way, and there's no explaining it now, but later one understands. And the trick is to let things unfold, rather than trying to force one's own will onto everything one comes into contact with. To let go of being in Planning My Life mode long enough to allow oneself to be visited by angels and surprised by joy.