You should have actual seat assignments at your wedding, even if you are having a very casual wedding. Having seat assignments help guests sit down quicker. Also you don't want guests feeling awkward by not having anyone to sit with.
Bathrooms. Yes, this is something you need to think about. Make sure you have enough bathrooms for your guests. You should have two bathrooms per 100 guests. Also, you will need to think about how the bathrooms will remain stocked and clean throughout the night. This is particularly important if you have to rent bathrooms for your event.
Food. If you forget everything else in this blog post, remember this. You need enough food to feed all of your guests! You should never run out of food at a wedding. Same goes with drinks. Although I have been to several weddings were they run out of beer, or wine, or the specialty drink. Just make sure you don't run out of alcohol all together. Also, when selecting food for your cocktail hour and reception, have a wide variety of options. You shouldn't only offer sushi and seafood at your cocktail hour, and only have crab cakes at your reception. Chances are some of your guests won't like seafood. You should mix up the food that is offered to your guests.
Communication. Communication is very important to your wedding guests. Make sure your invitations clearly spell out the important details of your wedding. Times, food options, transportation, and lodging information should be on your invitation and on your wedding website. You should also communicate if your venue will take place outside. Guests will need to know how to dress and what type of shoes to wear (some ladies prefer not to wear heels to an outdoor ceremony). If you are incorporating religious traditions into your ceremony, you should communicate this to your guests in your ceremony programs. Example: If you are Jewish and will be breaking the glass, explain what this tradition means in your ceremony program. It will help your guests enjoy the ceremony rather than be confused.
Last but not least- the married couple needs to say hello to everyone. Sometime during your reception you should get up and walk around to each table and thank your guests for coming. If you follow these simple rules I have no doubt your guests will leave happy!