It's a quick tip but one that will help keep everyone's sanity when the florist shows up with a box o' buds and is trying to figure out who gets what.
a) If someone is going to have personal flowers (ie boutonniere, corsage, bouquet) let them know ahead of time so they are aware of it and can be on the look out for the flowers on the wedding day.
b) Send a list to the florist (or coordinator) of who receives what so they can make tags to go on each posy. This way, everyone knows who is missing what flowers.
c) assign one groomsman and one bridesmaid to be in charge of guy's and gal's flowers, doing a doublecheck that everyone who needs a posy has it.