The key is anticipation. If a light goes up, be ready with any flags or stands that it might need. If it's your first feature as a grip, you probably haven't developed the eye for lighting to know when a light will need a topper, sider, lenser, etc. The main thing for you would be to know the equipment and as much about it as you can. Get a catalogue from Matthews, or American if you can and study it. Learn names and what each piece looks like. It will seem like a lot to digest and it is, so don't get discouraged. Gripping involves a lot of areas so just do the best you can and try to absorb what you can. For now, I would do the basics: If a light goes up, have at least a flag and stand set aside ready to run it in. If your key is setting something, make sure he has a shotbag, if dolly track is being laid, know where the wedges are and be ready with them. Above all, ask questions. We all started where you are now. Have fun. If you get sent to the truck for a "board stretcher" they are usually kept in the jockey boxes.
Good Luck,
ghard