There was this exchange between Picard and Riker in TNG'S "Next Phase" in which everyone thought LaForge and Ro were dead:
PICARD: Commander, there'll be a memorial service at twenty three hundred hours this evening. Mister Data is making arrangements.
RIKER: I'll be there.
RO (phased): Me, too.
RIKER: In fact I might like to say a few words.
PICARD: You did know LaForge longer than any of us.
That last bit suggests that Riker and LaForge may have served together before the Enterprise, likely on the Hood, IMO.
PICARD: Commander, there'll be a memorial service at twenty three hundred hours this evening. Mister Data is making arrangements.
RIKER: I'll be there.
RO (phased): Me, too.
RIKER: In fact I might like to say a few words.
PICARD: You did know LaForge longer than any of us.
That last bit suggests that Riker and LaForge may have served together before the Enterprise, likely on the Hood, IMO.