I have no idea what to do for my center pieces

My wedding is in June and our colors are yellow and green. I'm having daisies, tulips, forsythia, and lillies (as far as I know). First off, should I go with silk flowers or real flowers?? I want real flowers for the bouquet. Also, what should I do for the center pieces that will be simple, yet elegant?? I have absolutely no ideas so any suggestions would be appreciated!