Picture is worth a thousand words...

Corny I know... but as I learned the hard way this old saying definitely applies to wedding planning.  You can explain what you want to your vendors til you're blue in the face, but that doesn't mean they'll actually get it.  And you'll have no way of knowing if they did or didn't until the big day.  Make it a priority to find pictures of bouquets, hairstyles, cakes, etc that you like, and make sure your vendors have them.

Also, if anyone is willing to make a mock-up of what they plan to do for the big day or if they've done something similar before, get a look at it!  And if all else fails, just remember that as long as you end up wed at the end of the day, that's what really counts.