Hi,
RFC two-seater fighter/reconnaissance squadrons were using formation flying from around middle-late 1916. One of their favourite techniques when attacked by large numbers of enemy scouts was to form a "defensive circle". It worked well with machines like the FE2, in which the observer (in the front cockpit) and the pilot behind him each had a gun of his own. They would cover the tail of the machine in front, that one would cover the next one's tail, etc, until the circle was complete. Then the whole formation, keeeping its circle, would gradually edge its way towards the British lines. When the later FE2D came in with a third (observer controlled) Lewis gun on a pillar that could fire back over the top wing it was even more effective. The Canadian/RFC/American flier
Harold Hartney describes it all very well in "Wings over France", and at one point mentions the German Scouts attacking in rigid formation, and being very easy to beat off when they did so.
I have also read some original Squadron Record Books at the Public Records Office at Kew, London, where the Recording Officer mentions the enemy being beaten off partly because they (ie the British pilots)Kept their formation well.
I imagine the same sort of thing applied to bomber units.
I believe that when the Bristol Fighter replaced FE2's in the F/R role they started off with similar tactics, but changed them when they realized what a good fighter they had.
Hope that helps.
Bob