At the desk
Keep the lamp clear of your working area. Think about shadows as you write or use a keyboard, and keep the switch within comfortable reach.
Beside the bed
Allow room for a book and the objects already on the bedside table. Check the shade position from where you sit or lie down, rather than judging it while standing.
Beside the sofa
A floor lamp needs space for its base as well as its shade. Leave a clear route around the seat and allow for furniture that moves.
In a living-room corner
Consider the corner from the rest of the room. Check the socket location and route the cable without crossing a walkway. Follow the lamp instructions for clearances.