Once you have a general topic in mind, brainstorm 5-10 related search terms BEFORE you start your research. This will help you define your research question.
For example: Search terms for Frida Kahlo could include specific aspects of her work such as folk art or magical realism. Search terms for African sculpture could include related words or terms like mask(s), terracotta or terra cotta, soapstone; Search terms can also include names of people, events, or places: while researching Street Art you could use terms like Banksy, Berlin Wall, or Jean-Michel Basquiat.