Do stand during the ardaas (prayer). When in doubt follow the bride's family to know when to stand or sit. Do enter the ceremony site in a line and bow as a sign of respect to the Guru Granth Sahib. Your forehead should touch the ground when you bow. Do take your shoes off before entering the ceremony site. There will be a basket for everyone's shoes. You can keep your socks on.
Do not stay confused. Ask questions and follow the bride's family on knowing when to stand or sit. Do not enter the ceremony site and sit down without bowing. The ceremony site is essentially the home of the Guru Granth Sahib (living guru/word of God). Do not enter the ceremony site with your shoes on.