Save a search.
In the pop-up window, select "Lock this search" and whether to include families, then choose the number of review sets to divide the search into.
Navigate back to the saved search that you locked and distribute your review sets by clicking "Run" next to each set and assigning the resulting review set to a user.
The documents contained in that set will now be visible. From the bulk action tool, select the document set you wish to assign. You can also toggle to include families.
A prompt box will open where you may select whomever you would like to assign the set. If the user is not on the list, they will need to either be created or added to that specific project. More information on users may be found here.
Tips and Tricks
If desired, you can divide a review set into smaller review sets. Just run a review set, then save a new search and split the review set further.
You can edit the name of the review set to the name of the person that will be reviewing these documents so that the user may quickly see which set she is responsible for.