1. Dress appropriately: Try to dress appropriately to show respect for the wedding and wish the bride and groom well.

2. Respect the elders: respect the elders, follow the traditional wedding ceremony, and don't make disrespectful and unfilial behaviors.

3. Entertain guests: Entertain guests warmly and leave a good impression on them.

4. Obey the wedding banquet procedure: Obey the wedding banquet procedure, and don't speak or make inappropriate behaviors first, so as not to affect the atmosphere of the whole wedding banquet.

5. Respect the bride: respect the bride and don't make her feel embarrassed or uncomfortable.

6. Don't be too indulgent: Don't be too indulgent in your words and deeds at the wedding banquet, so as not to affect the image of yourself and others.

Generally speaking, as a brother-in-law, he should be decent, respectful, polite and enthusiastic at the wedding banquet to show his blessing and respect for the bride and groom.