A private practice server is the fastest way to learn smokes, flashes and map angles. Here is how to set one up.
1. Enable the console
Go to Settings > Game and set Enable Developer Console to Yes. Press ~ to open it.
2. Start an offline map
Start a Practice game with no bots on the map you want to learn.
3. Enter these commands
sv_cheats 1enables practice commands.mp_warmup_endends warmup.bot_kickremoves bots.sv_infinite_ammo 1gives unlimited grenades.nocliplets you fly around to learn positions (type it again to turn it off).
What to practise
Learn two or three smokes per bomb site on your favourite map: one to cross a dangerous angle, one to cut off rotations, and one for retakes. Learn them from both sides. Then practise one flashbang that lets you peek safely.
Cheat commands only work on servers you control. They do nothing in matchmaking.