Reading the New York subway map
Three things decide whether you get where you're going: the direction (uptown or downtown), whether the train is express or local, and which of the trains sharing your colour you actually want.
Colours are trunk lines, not routes
This is the thing that confuses newcomers most. A colour is a shared trunk through Manhattan, not a single route.
Blue is the 8th Avenue trunk — the A, C and E all run on it. Green is Lexington Avenue — the 4, 5 and 6. Red is 7th Avenue — the 1, 2 and 3.
So "take the green line" is not enough information. You need the letter or number, because those trains diverge once they leave the trunk.
Uptown and downtown are the platform, and getting it wrong is common
Signs and platforms are labelled Uptown (north, towards the Bronx) and Downtown (south, towards Brooklyn), not by destination the way many cities do.
Street numbers rise as you go north. If you're at 14th St heading to 42nd St, that's uptown.
Many stations have separate entrances for each direction, with no way to cross over once you've tapped in. Read the sign on the stair before you go down. Getting this wrong costs you a fare and a walk across the road.
Express skips stops — check before you board
On the map, filled black dots are local stops; white dots are express stops.
A local stops everywhere. An express skips most of them, which is fast if your station is an express stop and infuriating if it isn't — you sail past your stop and end up thirty blocks away.
If you're not sure, take the local. Slower beats lost.
Trains change at night and at weekends
New York runs 24 hours, which means maintenance happens while trains are running. Late nights and weekends, expect express trains to run local, some services not to run at all, and trains to be diverted onto other lines.
There are posters at stations and announcements on platforms, but the honest answer is to check a live app before travelling at odd hours. A printed map is a picture of the intended service, not tonight's.
Check the letter on the front of the train
Several routes share a platform. The train's route letter or number is displayed on the front and the side of the train, and announced before it departs.
Don't board just because a train arrived at the platform you were told to use. Look at the letter. On a shared platform the wrong one comes just as often as the right one.
Lifts are the exception, not the rule
Most stations are stairs-only. If you have a pushchair, heavy luggage or difficulty with stairs, plan the route around accessible stations rather than assuming.
The map marks accessible stations with a wheelchair symbol. There are far fewer than you would expect, and an out-of-service lift can strand you. Check before you set off with a suitcase.