1) At the station
You'll find all signage, including the self service machines, is in both Czech and English and the directional arrows to the different metro lines are all color coded so don't worry about a language barrier.
Validate your ticket or pass when you pass through the gate to the metro and hold on to your ticket until you have exited the metro as ticket inspectors may ask you to show proof of purchase.
2) Find your train
To find your train line just follow the colored directional arrows and signs. As each line has trains going in two different directions, check the directional map on the wall to make sure you're heading the right way.
3) Exiting the station
Once you've arrived at your final destination, find your desired exit and insert your ticket into the turnstile to leave the station.