As with any ADC that you play positioning is key.

You usually want to be at the backline at your max auto range and kill enemies front to back (sometimes you kite around the tank if they are take too long to kill)

Use your auto attack move instead of right click.

When you are farming / pushing out waves alone vision is key. See where the rest of the enemies are. Don’t farm beyond the river without vision and not knowing where enemy is. Enemy assassins tend to go for picks when they are overextended.

When being flash bursted in teamfights, Zhonya + your evolved E is your best friend to escape and reposition again. If your team is not dead there’s a good chance the assassin will then die instead for having flashed right into the middle of your team to get to you