All publishers are different. These tips are very broad and general things that I have noticed over many years of reviewing thousands of submissions. For me, the magic is in the details.
Be familiar with the publishers guidelines.
Send only your best work in for consideration. Publishers listen to hundreds of pieces of new music in a season. Show them only your very best
Field test your work before submitting. Having a live band play through a work can be very helpful and prevent embarrassing oversights.
Make your score look as clean and consistent as possible. Are dynamics marked clearly and consistently? How about articulations? Are rehearsal marks at regular intervals? Are Percussion instruments listed, labeled and well organized?
Cover letters are your opportunity to give the reviewer insight into project. What inspired you to write it? Is there a particular story behind the music? Is there a teaching strategy or curricular need that is being addressed? Why would anyone be interested in this work?
Not all publishers take unsolicited submissions. Check their websites for details on how to submit and follow the directions carefully. Make sure all requirements are met and be sure you are sending the correct piece.
Do not be discouraged if your piece isn’t accepted right away. Publishers balance a complex puzzle of roster needs, thematic fits, and seasonal timing—meaning even brilliant pieces get passed on simply because they don’t fit the catalog at the time.
If you have more questions about this topic, reach out via my contact page.
Wishing you the very best as you share your talents with the world.