Fantastic thread of ideas here, please keep 'em coming!
I think that starting in a general way with attention, humility (i.e., strong interest in learning and development), and wide open eyes allows intentions to naturally become more specific in ways that are likely to work. For example, instead of Jane in accounting to start out with, an intention for "a meaningful relationship" (nice but pretty broad and with no specifically articulated context to the person intending or that person's current environment and circumstances) may well lead to an intention to "naturally and consistently understand what it takes to develop meaningful relationships". That one may lead to an intention to "interact on a daily basis with others in a loving, compassionate, humorous, fun loving, sincere and interested manner which leads me to recognize people who will become truly meaningful to me as I get to know them better', just for example. And then, as Jane (or somebody else) is found to repeatedly make eye contact and smile, well then perhaps an intention to "maintain confidence in my interactions with others so that it is easy to meet people and see what they are about" and so on!
Now, since we have people experiencing success with parking places, perhaps the idea of Jane is not so far fetched. Then, perhaps a specific intention that Jane looks up with smiling eyes might lead to an intention that "when Jane looks at me I easily and confidently smile at her and project both interest and openmindedness, while at the same time, trusting (God, the universe, my intentions, myself) to notice the right things and interact positively.
Just some thoughts to add to this great thread. I agree that in most cases hard work (yah, even in relationships) is important and the love of hard work along with the choosing of meaningful hard work is essential. There's another intention brewing in that, isn't there/
Last, I think the most powerful intentions boil down to things we become able to change in ourselves, and often when we think we are just lucky or have manifested a material thing, we have in truth manifested an improved state within ourselves--attention, positive thought, easy natural positive interactional skills, love for others, concentration, discipline, the ability to recognize and put to good use opportunities that come around our radar screens.....