Every party has its own "personality" that is shaped by a number of elements.  Certainly the atmosphere of the location and the quality of the food service will have much to do with your party's success.  A guest list that includes experienced party goers with a well developed infectious sense of fun and an inclination to dance is one of the secret tricks of successful hosts.  But it must be emphasized that good entertainment can overcome the lack of all those things (and very often must).  If I think my services will not be suitable for your affair I will not accept your booking and will advise you of other more suitable possibilities. 

Let's look at the fundamentals:
	What kind of party are you having? I know it seems obvious to most, but  what sounded so great at that wedding you went to may not cut it for the Bar Mitzvah you're planning. Look for experience in your type of affair.  The guy you heard perform successfully at a 50th wedding anniversary may well be even better at your "younger" affair because of the number of them he has already done.  And what was fun at the office picnic may seem hokey at the club.
	The Master of Ceremonies The skills required for this have everything to do with the type of party. A wedding or Bar Mitzvah almost always should have a good MC with plenty of crowd material (line dances, games, mixers, etc.) along with a working knowledge of the traditional requirements of the affair. The same could be said of the "big" anniversary parties.  Country Clubs and Society Events always call for a much lower key approach with little MC'ing at all.
	The Music This can be trickier than you think.  The 85th birthday party you're planning may seem to call for music for an 85 year old, but what if the nearest age group to the guest of honor are those in their 60's? You need music for the grandchildren too.  Good entertainment is versatile!  Good entertainers play what everybody can dance to.  The task is to create a "psychological crowd" of your guests for a shared experience.
	Special Events Freilachs, Tarantellas, Jigs, Reels - ethnic music where appropriate (virtually forbidden in Country Clubs). Special Music - most weddings, for example, have an introduction, first dance, toast, a dance with Mom or Dad in addition to songs with a peculiar sentimental value to the new couple. Patriotic & Holiday Music for those occasions that call for it. These are merely a few examples of what experienced entertainers must be ready to produce on demand.  They can help you anticipate this.