The organization of the camp around the Mishkan was given by HWHY. I see that Rachel's son and grandsons' tribes are camped by the West under the command of Ephraim.  This is a place of honor because it covers the rear of the Mishkan in case of a sneaky attack by a treacherous enemy. Rachel's surrogate sons by Bilhah are camping by the North under the command of Dan (including Asher who is Leah's surrogate son by Zilpah). 

 

Leah's sons are camped by the East under the command of Judah  and by the South under the command of Reuben plus Leah's surrogate son by Zilpah Gad. This also signifies that Judah, whose name means I will praise YAH, guards the only entrance to the Mishkan and is first in the order of battle. So the praises and worship team lead the whole assembly as it ought to be.

 

Levites, who are the sons of Leah, serve the Kohanim and dismantle or assemble the infrastructure and the covering outside of the Mishkan.  But the Kohanim are in charge of the set-apart utensils and fixtures from the inside of the Mishkan.

 

In terms of numbers, the strongest camp is under the command of Judah and the smallest camp is under the command of Ephraim.  

 

When a single silver trumpet is heard making a tekiah (joy) blast then the princes and heads of the thousands shall gather and congregate by the entrance to the Mishkan. When both silver trumpets are heard making a tekiah (joy) sound then the whole assembly shall congregate by the entrance to the Mishkan. When a silver trumpet is heard making teruah (alarm)  sound then Judah's camp assembles for battle and goes forward.   When a second silver trumpet teruah (alarm) sound is is heard then Reuben's camp prepares for battle and goes forward. But they shall also blow an alarm for their journeys.

 

Num 10:7 But when the congregation is to be gathered together, ye shall blow, but ye shall not sound an alarm. 
Num 10:8 And the sons of Aaron, the priests, shall blow with the trumpets; and they shall be to you for an ordinance for ever throughout your generations. 
Num 10:9 And if ye go to war in your land against the enemy that oppresseth you, then ye shall blow an alarm with the trumpets; and ye shall be remembered before the LORD your God, and ye shall be saved from your enemies.

Num 10:10 And in the day of your gladness, and in your appointed times, and in your new moons, you shall blow the trumpets over your burnt offerings, and over the sacrifices of your peace offerings. And they shall be to you for a memorial before your Elohim. I am YAHWEH your Elohim.

 

Note how interesting it is that in the arrangement of the camps and the order of battle, a parallel exists in that Jacob is protective of Rachel and Joseph in Genesis 33:2. Note also that Reuben prevented his brothers from killing Joseph in Genesis 37:22  and note that  Judah  offered himself to pay the price and become a slave to Joseph in Genesis 44:33  to save Benjamin.  And so both Judah and Reuben have preeminence in the order of battle.