Using this radar image of cs_office, we can see the locations of the four smokes that this guide covers. Two of these smokes are "one-way" smokes, meaning that visibility is significantly better from one side of the smoke, which can be very advantageous. These "one-way" smokes have been marked with arrows, which you will be positioned at the back (flat) side, and the enemy CT player(s) will be at the front (pointy) side.

This is a great smoke for slowing down the CT team. Even with the best possible spawn, a CT will never make it into side hall before the round timer at the top says 1:40. I wait until about 1:35 to throw this. To line this up, just back into the corner between the plant and the wall, aim your crosshair at the corner where the floor meets the walls, and left click.

What's really nice about this placement is that you can see if an enemy tries to go through the smoke to hide in the corner.

For this smoke, walk about halfway out into the hallway from the corner by the vending machines and aim at the lamp in bathrooms and left click.
This will result in a smoke that you can see feet under, but the enemies can only see through at the leftmost corner.

This is a smoke that you want to get down at about 1:50, and it is very easy.
Stand back from the doorway, look straight ahead, and right click.
The enemies will most likely spam through this smoke, so be careful.

This is a good smoke if the CT team is trying to push elbow, or have thrown a smoke or fire into paper room. First, walk into the corner where these two bookcases meet.
Next, aim at the farthest part of the plant that is just around the corner.
Now left click. The smoke will land on the farthest chair.
You will be able to see under the corner of the smoke.
Anyone on the other side will not have the same ability.