The first question we must answer in knowing God's will is whether or not God has commanded us to do it. If He has called us to a task we should not continue to ask if this is His will. It is. He has already said so.
The next question is for most of the other things we do. These are the things where we seek His will but are not really sure because we know that we can find a scripture or a sign for just about anything we want to do. Thus, we can't even trust ourselves in determining God's will.
The question is: Will God be with me in what I am seeking to do? Of course, you should know that He is with you right now before you ask that question. If you don't know His presence, you should seek Him with your whole heart. You must seek Him until you know His presence. Then, you will be ready to ask whether He will be with you in what you desire.
There has to be a trust that is developed. You trust Him with all your heart. Thus, you can trust that He will answer your prayers. You can trust that He will bring about anything He has desired for you. You can know you have victory before the battle begins.
God told Joshua that He would be with him in the taking of the Promised Land. He told the Israelites that rebelled against Him that He would not be with them when they decided to go to take the Promised Land. It is clear that God's ultimate purpose was to give this land to His people but those who would do so needed His presence. The lack of His presence assured defeat.
Personally, I don't even want to start something that is guaranteed defeat. Why would I want to do something without the Lord?
Sometimes Christians make decisions as if it is the next logical step. They see the extension of church buildings or even the beginning of a mission as things that must be the will of the Lord. After all, doesn't He want us to reach people? Wouldn't it all be easy if you could just put things in categories like that? No, the Promised Land had to be taken with the right people at the right time. And so it is with a church or a person.
So, the real question is whether or not God will be with us when we do what we would like to do.