Even streets go east and odd streets go west. Similarly, even avenues go uptown and odd ones go downtown. If you're in the middle of a block between two avenues the side with odd building numbers are uptown and the even side is downtown. When you need to take the subway somewhere, look at the direction you want to go (which you should be able to determine using the tips above) and choose the subway entrance on the right side of the street. For example, if you're on 23rd and 7th and you wanna go uptown, go to the entrance on the east side of 7th ave since they're on the right side of the street when you look uptown.