It's not good enough, to get on your knees and say, "Look God this is what I want to do. Is it okay with You?" . . . one time. Come on, if you really want to know God's will, you are going to have to let Him show you the best way to act.
The next thing that Nehemiah did was go to the king and ask permission to go. Sometimes we decide something is important and we also decide that WE know how to go about it. Most all of us have obligations (ie: jobs) and we can't just go off and do whatever we "feel". We can't just run away from our responsibilities. Neither could Nehemiah. He had to ask permission from the king to go home and help out.
Then the next thing Nehemiah did was go and check out the damage to the walls of the city. So what should our next step be in tackling the impossible thing that God wants us to do?
Check it out! Take a look. Assess the situation. Study it. How can you do something without knowing what needs to be done.