Be nice.
Some touring DJs do not need to be booked over an agency. If you can find their website and shoot them an Email directly they also will answer and you can circumvent their agent fee. Some will insist on their agent, due to their contract.
What I like when someone books me:
Piloteness.
Include the date and details on the venue. (Is it a club, how big, is there a backstage area, do I get a room or do I share with other DJs in the backstage,….)
Include details on how you want to arrange for travel an stay. Usually you can have it either way, if you have a discount at a hotel that I will not get, you prolly are off cheaper if you book it, same if you want flights booked etc. as I will simply go book a flight that suits me and bill it to you, or in case I can get there via train or car charge you whatever that costs.
If you are booking the hotel for me, I would want to know what it includes. (I one time ended up in a hotel near a train station, that was loud as hell and had to share a toilet with the whole floor…. I never make that mistake again and trust someone who books me hehe)
Tell something about your event and what you expect: Aka what other DJs are you in the process of getting, what equipment will be at the venue and what sort of set do you expect me to play.
End with some nice words why you have chosen me and we are in business….
It is rare that I get something in this quality when I get booked, but when it happens I feel much more obliged to answer and attend and cut a better deal.