If you have students that are new to studying Spanish, begin assigning lessons from Core15. Core15 lessons are written with the most limited set of vocabulary. Continue on in numerical sequence from there, assigning lessons from Core25, Core35, Core45, etc.
If your students have already begun their Spanish learning journey, look at the Path Description for each path in order to see which new words are introduced and which ones are recycled. Choose to begin assigning lessons from a path that uses mostly words that your students are familiar with, then move forward in the Path sequence from there.
If you are using the SOMOS Curriculum, simply filter lessons by the Unit number in order to find materials that fit well with that unit.