Event Design to me starts with the overall flow of the event itself and can then work backwards to what happens prior to the event, and / or forward to post event, but needs to start with the purpose of the event in the first place and how you want the Day (s), Night(s), Weekend to work. As I have mentioned elsewhere on this site, the Flow of the event is where I believe it all starts. This is generally about the location but of course depends on whether you have selected a venue or location or if you are trying to find somewhere that will fit in with you.
Work out the must / need to haves. These are not always things that you necessarily want, they may be limitations of the venue, the caterer, the entertainment, the birthday boy or the mother in law… Don’t fight against a location, work with it. There are usually a number of solutions to any hurdle and some of them are more important than others to you. Everyone has their thing that is important to them and sometimes you won’t even know what this is until it comes up. Do not be afraid to speak up about anything that you do or don’t like, it is what will make your event truly unique to you.
When discussing your event with an Event Designer understand that it is a collaboration that requires open discussion to ascertain what it is that you want it to look and feel like. Some of the advice that you receive may be sound, but at the same time might not be important to you.