Please please please make room in your budget from the get go with room for at least a coordinator for the month of the wedding. And your best friend and Aunt don't count! If you want to stress on the wedding day, then you can throw this tip out the window but if you'd like to have a peaceful, stress-free most wonderful day of your life, please listen to me. A coordinator will help you create a "clearly defined timeline that is set up for success. Having a wedding planner and strong DJ will ensure this is handled." (Hey Mister DJ) I am a coordinator and I hired a coordinator...let that sink in!
2. Hiring your friends
It is a lot easier to tell a hired vendor "no." And while hiring professionals is imperative, I get that some of your friends and family may be professionals in the wedding industry. Does this mean you should hire them? Absolutely not. If you don't like your hair or the photos don't turn out to be as you had imagined, it is going to be quite the awkward friendship moving forward. So keep your friends as your friends, and your vendors as vendors. You can make friends with your vendors too though ;)
3. Forgetting to tell your photographer about important photographs
"Bring a box. Put your coordinator in charge of giving the box to your photographer while you're getting ready. Fill it with important details you want photographed like your invitations, save the dates, family heirlooms, something blue, accessories you're wearing that day, wedding rings, parents' wedding photos, bridal party gifts, letters...And make sure you tell your photographer if there is a special moment or object you want photographed." (Britt, From Britt's Eye View Photography) Vendors cannot read your mind!
4. Letting anyone give you input on the dress before you express your own opinion
When you are trying on dresses, the rule is that anyone with you cannot say how they feel about each dress until you have stated your opinion. If you hate it, state it and move on. And if you love it, love it with pride and shout it out loud. And if you do that before anyone else says anything, they are far less likely to give you their "true" input and willbe there to support you and your decision.