Being a bridesmaid is an honor, but it's also a job. It's definitely work. Look for practical, hands-on ways to provide acts of service. For example, the bride probably will be busy enjoying herself and visiting with family at the rehearsal dinner. If a table is shy a seat and Uncle Larry is left standing, find an extra chair and help him get situated. Mingle, introduce guests to each other, keep the bride's and groom's glasses full.
Take loads of photos throughout the wedding-planning journey from the early days of dress shopping to the last hours at the reception where Nana hit the dance floor and learned the Macarena. When it's all over, the bride shouldn't be the one to call a taxi for her wasted younger brother and his date. That's all you. Taking over some of the grunt work will be much appreciated.