1.) Start with a research question: Is animal testing ethical?
2.) Question your question. Does your question raise more questions?
3.) Once you start your research process, consider your subject terms. Think of synonyms/alternate/or related phrases.
4.) Can you narrow your topic? For example, animal testing may be conducted for scientific/medical or commercial purposes. Maybe you wish to focus on medical testing?
Or perhaps you wish to focus on animal testing for consumer products? Maybe you wish to go even more specific-- perhaps you wish to focus on animal tested cosmetic products?
5.) Return to your research question. You may find that the question has changed: Is animal testing in the cosmetic industry ethical?