Hi, Samantha! When I used to do a lot of gigs, I would assemble the music in my binder to go with the type of job it was. I liked to mix it up, so that I would go from one genre to another. If you use different-coloured tabs inside the binder, you can label these with whatever categories you want, so that you can flip back and forth from Celtic to contemporary pop, to classical, to old standards, etc. If something straddles the categories, you could have multiple copies, one with each tab. I hope this helps!
I use an iPad and have different playlists in it grouped by genre. My booking form has a tick box section where people choose the types of music they like so I choose my playlists depending on their preferences. If I’m left to my own divices I tend to start with more classical repertoire and gradually move through folk/celtic and into lighter stuff – films, musicals jazz and pop – as the evening moves on.