If you take the manhattan bridge, it's easy, just ride over the right side, keep going straight when you get off (should be down jay street) for 3-4 blocks until you get to the huge intersection where NY tech college is, make a left until you get to flatbush, make a right to go down flatbush, go down that until you get to 4th or 5th avenue and make a right to get on that, keep biking down until you get to 3rd street and go up that till 8th ave.
Don't take 1st, I think 2 sections of that are under construction and it's completely torn up for 2 blocks.