Are you planning to do the memorial ride tonight @ 6? If so we can ride back together, I live in Park Slope, right around where you are going... PM me if you want.
Otherwise, Slvoid's directions are good (take 5th Avenue... 4th is like a madhouse). I prefer the BB myself, once you exit in Brooklyn, keep going straight past the intersection with Atlantic and make the next left (Dean I think) all the way to 5th Avenue. I think the work on 1st St is completed so you may be OK...