Now that I'm going into the field of emceeing full time, I realized, there are certain points that distinguish professionals from those who just do emceeing for the fun of it:
a) professionals know and take to heart that a wedding is a once-in-a-lifetime event, so they get involved in the planning and help couples come up with the most appropriate program -- given their personalities and the guest profile
b) they look at all aspects of the venue so they know where to stand and when to introduce an AVP (for instance, if the venue is all glass and it's still sunny outside, showing an AVP might not be a good idea, especially if after a while, the sun will set anyway)
c) they share the limelight with fellow suppliers -- recognizing the important people in the background -- as they go on with the program (for instance, one can mention the cake supplier during cake cutting or the band when the dinner or party set is about to start)
d) they are more than aware of the fact that they are not the stars of the show, rather they make sure the bride and groom become the center of attention (because it's their day!!!)
e) they prepare for the program -- music is critical, cuing people with parts through the coordinators is also imperative, getting all materials ready prior to games is also important. They ask the coordinators about such matters and avoid leaving things to chance.
f) they work fast and encourage others to follow the schedule as well. Why? Because guests get fidgety. They don't want an empty ballroom by the time they announce the onsite.
g) they think of add-ons to make the program more thematic, more enjoyable for guests, etc.
h) they walk the couple through the program so that the couple knows what to expect and how to prepare for the program as well (materials, prizes, people with parts)
i) they leave no stone unturned to come up with a program that will be memorable for the couple
j) they come on time -- to do a run through with the coords in case there are changes/add-ons/deletions -- and they don't rush to leave because they space their receptions/bookings appropriately