Sometimes it is best to start searching form the search form for a specific data collection. The form tells you what has been indexed which is critical in understanding what to enter.
Take for example the US Federal Census 1850 search form:
Relationships are indexed, because they are explicitly stated, so you can’t use that as a search strategy.
On a census form, if you enter a county and stage from our type ahead for places and then choose exact, you will limit all of your searches to that county. Or you can choose adjacent county if you are not finding who you are looking for.
Also, you can set other fields to exact to limit your searches as well. By looking at the form, you understand what is actually indexed and this will help you choose what is appropriate to use as parameters in your search.