What belongs in your text
Add two to four short points for each job. Explain your work, not only your title. For administrative assistant, this matters when you plan meetings and organise emails. Write what you did, where it happened and why the work was useful.
A good example is a short account of how you maintain files and resolve questions. It shows real work rather than an empty claim. If you have not done that task, choose a different example from your own work.