Otherwise my best advice is to forget that you have 500 or 600 mm and get as close as possible to the birds without scaring them. I think that is the biggest mistake that most new owners make with longer lenses. They think that if they have longer glass that they do not need to get as close. I totally disagree. All of my best pics have been through close approach, good light and a steady hand. Very few of my large crops have results anywhere close to the shots when I was close.
Hope that helps.
the best accessory to a long lens is a camo suite and stalking classes ;-)