When working via internet I prefer to work with artists, producers and co-writers who own a DAW and know how to record, themselves, export stems and convert to various file formats.
If you create lyrics and have a preconcieved idea for a melody that you prefer to use, be capable of singing on pitch or playing it on an instrument. Knowing the exact notes you intended will help me to put music to it. Anyone missing those skills must allow me to create a new melody. A well crafted melody can support the mood of the lyrics by using specific scales and rhythms.
Be flexible and allow for changes in your lyric when suggested by a co-writer. Input from others who posess the same skillset is a great way to polish your lyrics to perfection. It is also a great way to transform them into something totally different but more powerful. Lyric input from a music co-writer will help you shape your lyrics from a musical perspective.
Music: My best collaborations are with others who have a formal education in music. When colloborating with someone who is giving musical input I need to be able to discuss chord & scale structure, song structure, progressions, hooks, rhythms and dynamics. Anyone who doesn't have this education, but is willing to learn, will also make a good collaboration.
Audio: A knowledge of acoustics of music and audio engineering will allow me to communicate well with co-producers and engineers.
I prefer to work only with people who posess these qualities:
Respects the skills and talents being brought to the table by others,
Welcomes input from everyone who is working together on a project,
Team player, always keeping in mind that we are all working for the team and not just ourselves.