You don’t have to put your desire out of your mind completely in order to manifest. However, if you do, you will manifest effortlessly. At the same time, this is not the only way to let go.
I have manifested in various momentary moods – during the sending of heart energy to my desire, after forgetting all about it, after letting it go only for a few minutes or hours, while expecting it to arrive any second or while simply feeling happy about it.
Don’t think about the process too much to avoid an attempt of controlling it.
Don’t think about “the right way of thinking” at all – just love your desire, live your life and enjoy various manifestation moods connected to it. As long as you believe, you will manifest.