The merciless intelligence driving the Borg is constantly looking to perfect their biological and technological superiority by assimilating other species and technologies. These directives are represented in the Borg Assimilation game expansion with the Borg Command deck.

 The Borg Target the Klingon Starbase

During the Borg game turn each player, in turn order, will pick a Borg Cube in play to activate. First the Cube will Engage Player Ships in Space Combat. Then, if the Cube is victorious, the player will draw and execute a Borg Command Card for the Cube. Finally, if the Cube is in orbit of a Developed System after it executes the direction of the Command Card, it will attempt to assimilate the world. After that, the player will place a Borg Activation Token on the Cube to show that it has been activated and then the next player will choose a different Cube in play to activate until all Cubes have been activated in the turn.

Borg Command Cards - Move::Target

The majority of Borg Command Cards will direct the Cube to move towards a selected target. These targets may include Developed Systems, Home SystemsStarbases, or Starships. Most cards show a number of Warp Tokens; this is the number of systems the Cube may move this turn. The player moves the Borg Cube towards the target System on the most efficient route, moving the number of Systems indicated by the number of Warp Tokens. 
A few directives influence Borg movement:

Borg Cubes will travel along established Space Lanes, but they may establish their own Space Lanes and discover new Systems, just as if they were players, when necessary. Just like players, when a new System is discovered, the Cube’s movement ends.

A Cube is not compelled to move the full amount of Warp Tokens shown if it reaches its target beforehand. However, the Cube will focus on its current objective, for instance it may bypass Developed Systems if its target is a Starbase.

Like player ships, a Borg Cube may not move through a player’s ship and must end its movement in the preceding Sector. In this way, a desperate civilization may try to delay the Borg before they reach their vital worlds.

If there are multiple viable targets within range, the Cube will choose the target that is closer. If it is a tie, the cube will move towards the System controlled by the player with the lower turn order number (and in the case between a player controlled world and a neutral developed system, the Borg will target the player controlled system). So while the player with Turn Order Card 1 may get to choose which Cube to activate first, that player will almost always be the target of the Borg in the case of tie as well as other certain circumstances.
Borg Command Cards - Assimilation
Borg Command Cards - Aggression

A Sector may not contain more than one Cube. If a Cube’s movement would have it end in the same Sector as another Cube, it will stop in the preceding Sector or System and complete the rest if its turn if able. Then the player will immediately activate the adjacent Cube and it will perform all of its actions, even if the Cube had already been activated earlier in the turn!

There are more simple guidelines on how the Borg utilize the Transwarp Hub and how they explore and establish new Space Lanes in the Borg Assimilation rulebook as well as how the Command Card phase of the Borg Turn totally changes when a player becomes fully assimilated by the Borg. Beware the Borg onslaught when the Borg Assimilation game expansion for Star Trek: Ascendancy warps into our quadrant in Q4 2017!