Probably the best idea is to list everything you do/did at your job no matter how important it may or may not seem to you. There are duties that we do every day that may not seem like a big deal to you but could very well be to a prospective employer. A blank resume is like an artist’s canvas with no picture just a spot of color here and there. It does not tell us a story or give us any idea of what the artist was trying to convey. The same is to be said of a resume.
After you have finished your list of duties, then go down through the list and either combines the ones that are relevant to each other or take out the duties that are minor and leave them off. You want substance for each job. Also make sure you use terminology that everyone can understand. If you are going to use acronyms then make sure the first time you use it that you put the words in parenthesis so that the recruiter/hiring manager that reads it can be certain of what it means. There are so many acronyms out there that are identical sometimes it is not easy to figure out.
So there is some food for thought and hopefully it helps! Have a great evening!