Expressing intent is a major part of communication while driving. It is language agnostic — a mere wave of hand can help the other drivers to re-evaluate their decisions.
For instance - a common mistake I used to make was to apply brakes at the exact time I needed to. But a sudden brake would surprise the vehicle right behind me - as they get very less time to react to it.
How to do it right?
Apply a slight break - hinting them to get ready for a change in flow. Take a pause of about half a second to actually apply breaks. This heads up will help the other driver react to you better.
Slow down your car before turning- start moving it in the direction you want to turn a little. Observe how people around you are reacting to it. Chances are some vehicles might not notice it until after a while - preventing a suprise turn into a bad accident (pun!).
The normal expression of intent we do on a daily basis is to use the indicator or flash headlights.
Another one would be a horn - just to alert the other car of things like :
- "I'm tryna overtake ; Keep going straight ; Do not deviate."
- "Hey look over here there's a vehicle coming through"
- "MOOOOOVE IT'S AN EMERGENCY"
Expressing intent while driving makes you predictable and helps others decide their course of action well in advance.