The trick for me is finding the line between defining something to the point where I could see it clearly, but not define it so much that I am attached to that particular thing.
For example, if I wanted to manifest a house. I would get clear on the feelings that I want in the house. I might get down to the number of rooms just because I would feel roomy in a 3 bedroom rather than 2. I might even envision the colors on the wall just so I could get really clear on the feelings I want in the house. Now, if I find a house that has 3 bedrooms and the colors, but not the feeling, it's not the one. If I find one that's a roomy 2 bedroom with different colors, but I get the feeling I wanted. Bingo!
In the past, I've gotten down into to deep, deep specifics and by then I am grasping it so tight that I am not open to the full experience of what I am intending.
I've learned to say "For this or better" and "For the highest good of all." I, individually, do not know everything, but the Universe, well, it's got its eyes all over the place.