OK--
When you get out of Penn Station you are going to be on 7th Avenue and about 32nd Street. Behind you you will see Madison Square Garden and you are going to cross 7th Avenue and walk away from Penn Station and MSG. Walk down the side street and the next avnue you will come to is 6th Avenue. There are entrances for the N/R/W trains on 6th Avenue anywhere between 32nd Street and 34th Street. Take any one of the entrances down to the subway and follow the signs for the N, R or W train towards UPTOWN or QUEENS. Take the N or W train uptown and it is about 10 stops. You are going to get off at 30th Avenue in Astoria. (it is the stop right after Broadway so start getting ready) When you get off at 30th Avenue walk up 30th so the streets are going upwards and you will pass Athens Cafe at 32nd Street and Avenue is on 36th Street.
I know these directions may have been a little TOO detailed since you have been to NYC before but I figured it would help anyone else who might want to come for the first time.
Enjoy!! And if you are hungry I recommend the Avenue Meze