Music has often been described as universal and in many ways is just that. It brings people together, creates enjoyment and is often a topic of conversation that can be discussed with almost anyone as not everyone at your wedding is going to know one another. The music you select for your day in terms of the ceremony will, most likely, be different than anything you’d want to hear on the radio or purchase on iTunes. Songs for the reception obviously are a much different story but there are things to keep in mind in reference to both.
As for your ceremony, the music is usually broken down into several different segments: the prelude (what is played as people gather and get seated), what you want people to hear when your family is seated, the processional (a selection for the time when your fiancé and bridal party take their places and, most importantly, the entrance and exit songs. It is acceptable for the entrance and exit songs to be the same as they will just be played at different speeds. Before you choose any of those, however, it is wise to decide on what type of musician(s) you want so as to ensure they are able to play and are familiar with your picks.
You certainly are not obligated to choose the “traditional” music such as “Canon in D” or “Clair de Lune” as many songs that you hear on the radio, for example, can be beautifully transformed in a way that isn’t cheesy or contradictory with the tone of your ceremony.
As for your reception, maybe you have specific songs and opt to make a playlist or perhaps you just prefer a certain tone and the individual songs are not of importance. You need to decide whether you want a band or DJ, both of which have pros and cons. Depending on the tone you want and your budget (as typically they are pricier), bands create a more intimate ambiance and a professional one can play most songs that you find important (or at least are willing to learn them).
DJs are often used when you want more vibrancy and energy and the doubt that something can’t be played is eliminated as they can find absolutely anything. However, it may be difficult for them to change the speed and tempo of music in order to adjust to/accommodate how people are dancing.
Regardless of what type of musician (whether a pianist, violinist, band, DJ or anything else), the wise thing to do is have a run through prior to the day of your ceremony. If that’s not an option or you choose not to, you should at least get either a CD or video of past performances so you are aware of what is in store and will not be let down or look back with regrets.