Confession: I often start a research quest with a simple Google search. Keeping in mind that not all the information I find on the web is going to be reliable, Google is still a good way to get my feet wet with a topic and gather the relevant vocabulary I need. Then I can move on to a more targeted database search.
You stumble upon this article, and it peaks your interest. So you ask yourself:
Is there a relationship between gut bacteria and autism?
Step 1: Step 1: Break up this research question into two or three main concepts. Ignore extraneous words.
Step 2: Conduct an initial search with these words, and quickly scan the results.
Step 3: Using information from your initial search, add synonyms, acronyms, and variant spellings.
(gut bacteria OR gut flora OR intestinal microbiome) AND (autism OR autistic)