Finding genuinely useful related terms is more systematic than just brainstorming synonyms off the top of your head.
Start From a Clear Seed Topic
A well-defined core topic gives you a clear anchor to expand outward from into its related vocabulary and subtopics.
Look at What Comprehensive Content Already Covers
Reviewing thorough, well-ranking content on your topic reveals the related terms and concepts a complete treatment of the subject naturally includes.
Organize What You Find Before Using It
A raw list of related terms is more useful once it's grouped into the specific subtopics or sections they actually support.
Next step: Use the LSI Tool to generate a structured list of related terms for your seed topic in one pass.