DO meet with clients directly.
It is a good idea to have a face-to-face meeting with your client if possible. This way you can meet them and get a feel for not only their wants and needs for the event, but also their personality. You want to have a good idea of the kinds of things they will like or dislike before you begin the planning process.
DO be present for the entirety of the event.
This includes set-up and take down as well as being at the event itself. If you are unable to be there, make sure one of your other planners or associates can be. You never know when something will go wrong and a tiny issue can become a big one if the planner is not there to sort things out.
DON'T use the same vendor for every client.
Even if you work very well with a particular vendor, it is important to consider your client's needs. Not all styles and personalities mesh well together. For example, a photographer whose aesthetic is very traditional might not be the best choice for a young bride having a nontraditional barnyard wedding, just like a caterer known for innovative and out-of-the-box culinary creations might not be the best choice for a dinner event for which the client wants standard beef or chicken plated meals. Having relationships with a handful of each kind of vendor- florists, DJs, photographers, etc.- will ensure that each client can be matched with the best vendor for them and the event they have in mind.
DON'T count on everyone else to break down and clean up.
Even though it is the job of each vender to pick up after themselves after the event, as a planner, it is your job to make sure the venue is back to perfect condition at the end of the night. This usually means staying at the venue until all the vendors leave to do a final check and make sure everything is back to the way it looked when you arrived.
There is nothing worse than a group of people at an event that have nothing to do. From the moment guests enter the event space, they should have something to occupy themselves, whether that is drinks and hors d'oeuvres, cocktail tables to gather and chat, music to listen to, or an activity such as a casino game; it is vital for those attending the event to feel comfortable. Often times larger events have many guests who may not know each other and it is much easier to break the ice in a big crowd if there is a specific activity at hand.
Above all, the biggest DO is to make sure guest are enjoying themselves. If you keep this in mind throughout planning and directing, you should find yourself cleaning up a successful event at the end of the night.