If you are starting your search, trying use keywords, rather than full sentences.
If you are searching for a phrase, such as model-based reasoning, put the entire phrase in double quotes. This will tell the database to only find results that contain the exact phrase, rather than one or two of the individual words.
If you have two or more words or concepts that you want to find, use AND (must be capitalized) to tell the search engine to only look for items that contain both words.
It's helpful to think about different terms that researchers and authors might use, and then to combine them with OR. For example, in the US we call the period before birth "prenatal," while in the UK they call it "antenatal." So if you wanted to make sure you got all possible articles on the topic, you'd type in (prenatal OR antenatal). Terms can also change over time: for example, if you want to find all the articles on ADHD written over the last 20 years, you'd want to enter (ADHD OR ADD), because ADD used to be treated as mostly separate from ADHD.
If you're having a really hard time finding relevant articles, and you're using an acronym of some sort, try spelling it out. So ADD would become Attention Deficit Disorder.