Before the game
Shake hands or offer a simple greeting before the clock starts — it's a small habit that sets a respectful tone for the game, win or lose. Arrive with your phone off or outside the playing hall entirely; most FIDE-rated events treat a visible phone as grounds for forfeiture regardless of intent.
During the game
Keep conversation with spectators or other players to a minimum during your own game, and never discuss a position with anyone while it's still being played, including your own. Touch-move is standard at rated level: if you touch a piece with intent to move, you're generally required to move it if a legal move exists.
Offering and accepting draws
A draw offer should be made quietly, after making your move, and only once per position unless the situation changes materially. Persistent draw offers after a clear decline are considered poor form and can be reported to an arbiter.
After the game
Sign the scoresheet, shake hands regardless of the result, and save detailed analysis of the game for later rather than at the board. A brief, gracious word to your opponent — win or lose — is one of the most consistent traits shared by well-regarded players at every level.