How can you tell if Jesus really is important in your life? It's simple really. When he is significant in every single part of it. Is your mind on God from sunrise to sunset?
Not just there, not just considered at a token level when you are choosing which school to send your children to. Significant means that he affects everything in a way that you couldn't do without, or that would see a totally different life if you were without consideration of Him.
And in every part of your life. There are no small decisions. Even down to the colour of your socks or the brand of cheese you buy. Jesus should be considered. Even if the answer is that it doesn't matter in this case, it is a habit that the Christian should be constantly building. Through this process you learn to understand the principles of Spiritual living which guide the "big" decisions.
The Christian life should be a closely examined life in many ways. Best we do the examining rather than waiting until Judgement Day where God will do the examining. It could be embarassing...