The trigrams are doubled like it says in the Da Zhuan (Wilhelm-Baynes page 325): "The eight trigrams are arranged according to completeness: thus the images are contained in them. Thereupon they are doubled: thus the lines are contained in them), but not necessarily by superposing two trigrams. Maybe by doubling every single line. In the Shuo Gua it says (W-B p.264) "..They combined these three fundamental powers and doubled them; therefore in the Book of Changes a sign is always formed by six lines."

Every station has its own properties, which have a direct relation with the trigram of that place.
E. g. top center is the station of trigram fire. When fire changes to lake (middle right, the station of lake), it does so through a hexagram.
                            
In order to change to lake , the middle and top line of fire change, so they are "old" yin and yang, respectively. Old yin is , old yang . The bottom line does not change, so it is young yang .

 

In this picture every "route" can be seen. From fire to thunder (center left) is hex.57, from fire to water (center bottom) hex.61.

So if you try to find out how to find a manifestation for your start (or: how to move from the thunder-station to the fire-station), go to the stations-picture, and look in the center-left station which hexagram figures in the center-top. This is hex.46. Step by step.. Or what can I bring in myself to make this start, which is the heaven trigram, bottom right? Hex.7, fight for it, organize.