Chossing a dj seems one of the easiest job in planning an event, be it a wedding or a party.
A party means all celebrations.
The dj should be up to date of all songs. For a wedding the bride and groom will choose songs to play for the first dance of the couple, the father daughter dance and most recently the groom and mother dance. Other songs are up to the dj unless requests are and should be accepted but this depends on the signed or verbally agreed contract.
If there are no requests "dj look around at the attendees" yes look. You should be aware of songs relative to age. This does not mean you must play many songs for attendees of older age but an occasional one, if you are uncertain ASK; you'd be surprise of the response.
If you should be dj ing for a specific culture say latin, or any other and see others attending ask if it will be okay to include a bit of diversity. Beleive sometimes including diversity can change your label of being a good dj, an okay dj, or just a bad dj and it is all because there is a lack of diversity.
To brides and all shopping for a dj of your moments and celebrations of memories ask one question, How diverse are you with your music".
DJ's get diversified you know your talent is great !!!