Nobody takes a late-comer seriously. Lateness is an affront to those who troubled to arrive on time. If you must cross your legs, do so at the ankles, otherwise, you look inattentive and altogether too casual. Make sure your shoes are polished and in good repair. Scuffed shoes imply a person ho disregards details.
Meetings are a place for team players.
Unless you are certain about how the seating arrangements work, ask your colleagues, introducing yourself to those you don't know and calling those you do know by name. Do this standing. If you are seated and a new introduction is made, stand up. Avoid confrontational language and public criticism. No matter how much you hate what the other person is saying, wait for the person to make their point before interjecting your opinion.