Do not entertain the thought of not receiving your desire. This is the problem. You must fully concede to your innermost self that whatever you desire is done. Start small. Record your results. Read over your positive stories. Manifest bigger. Bigger. Bigger. I am telling you, and I'd stake my entire existence and life on this, that it works. It works every single time. 

Just enter into a scene in first person perspective (look through your own eyes in the scene) and make sure it is at the very end of you receiving your desire. Repeat this until it is as real as it can get. Do not imagine the desire, imagine AFTER the desire. A scene which would embody that fulfilling. A scene that would happen IF and only IF your desire had been fulfilled.

Make sure you do this when you are not distracted. Breathing through the diaphragm will help to enhance the feelings. The entire goal is to make your imaginal act identical to one that would happen in real life if your desire was already fulfilled.

Feel the emotions of the end result. Experience the physical sensations of your desire being fulfilled. Like I said, it must FEEL REAL. 

Do this and repeat it in one sitting until it becomes real. And then release it. 

Your goal should be to practice stilling your mind and then entering your desire state. This should be your only goal. The way Neville Explains it is that he first sites and contemplates his desire for a few moments. Then he contemplates what would be an END to this desire which would happen IF and only IF it was fulfilled. After that, he closes his eyes and enters into a hypnotic state, which you can find a LOT of this on the internet (how to enter a hypnotic state). Then visualize the scene. When you move your hand in your imagination, you should be looking at it through your own imaginal eyes. 

Practice this every day, before bed, or during the day, whichever you prefer. Although if you do it at night your results will be certain, because your consciousness is shutting off and you are in direct communion with your subconscious mind, which is God.

A way Neville explains on how to practice this is to, before bed, when we are laying down, replay the events of the day in reverse order, starting at the time you just laid down until the time you wake up in the morning. Experience this through your own eyes, not as if you were watching yourself play a role on a screen. You ARE the character. As you replay these events, modify them to embody the scenes you actually desire to see. In doing so, you will be revising your day, and practicing how to visualize.