I usually run the cables without any "auxiliary" management if you will. The cables run gracefully as God intended, with the rear cable crossing and passing behind the front brake cable (just above the stem extension).

There are exceptions however, such as with centerpull brakes or the "backward" early Dia-Compe and Shimano (non-Dura-Ace) sidepull calipers.
On these setups, the cables do not usually cross (except in rare cases where the front brake cable perhaps passes to the right of the stem extension).

With stem shifters, I may tuck the rear brake cable behind the right shifter cable, against the upper headset, in those cases when it is routed along the right side of the top tube (Peugeot, Raleigh and Schwinn often did this).

I've even used a tiny loop of bead chain on a couple of builds.

Often some cable management trick is used to keep a cable housing from clinking noisily against the handlebar or even against the other brake cable!