While general customer service routine (smile, welcome, surprise presents, being positive, solving problems) is mandatory, it is also very important to evaluate your guests.
While you should assume that all your guests are nice, positive people of course, also keep in mind the probability that some might cause trouble, and try your best to identify potential trouble makers and type of problems they might cause.
Like this gentleman seems like heavy drinker-so keep an eye on him to prevent any problems which too much alcohol causes.
Or certain lady is dressed to light and pays too much attention to someones else's husband. Not your business of course, but keep in mind that someone in this triangle might explode and you or your staff member needs to be there in no time to calm flaming passions.
Same goes to criminal like individuals, football fans, over-zealot religious people, mothers with young babies, people who bring big animals, etc etc.
It is counter productive to try to block them from entry of make them feel unwelcome, but keep your eyes open