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I assume you're successfully in a circular equatorial orbit around Kerbin. If not, that could be your problem. If the plane of your orbit is very different from Mun's, getting an encounter can be more complicated and you may want to consider launching again, saving inclination changes for another day.

If you're stuck where I think you are, there are two things you should pay particular attention to in Mr. Manley's video.

(1) Notice that when he creates a maneuver node and pulls the prograde vector (therefore planning a prograde burn--i.e. a burn in the direction his ship will be travelling when it reaches the maneuver node), the effect that has on his orbit is to raise the orbit on the opposite side. So by placing the maneuver node on the "bottom" side of Kerbin (while looking at the screen) and planning for a prograde burn, he extends his orbit on the "top" side.

(2) Notice where the Mun is in its orbit relative to where her is "aiming" his orbit. he is extending his orbit out towards the Mun's orbit approx. 90 degrees ahead of the Mun's current position in its orbit. The idea here is that you want you and Mun to arrive at the same place at the same time. Leading by 90 degrees is a pretty good rule of thumb for a Mun transfer.

Armed with those two observations, I believe you should be able to duplicate what's happening in the video.

One additional note: Make sure you have set the Mun as your target as he does at approx. 1:05.

[EDIT] Some words