Grove Online is a great source for recent, reliable information on all topics related to music. It is also a good starting point for research since one has the ability to browse the bibliography of sources used to write the article in Grove. Do not be afraid to springboard to other sources from the Grove bibliographic information.
Similarly, although Wikipedia is not always the best source for scholarly information, it is not a bad starting point. The Wikipedia bibliographic information can also be used to find more appropriate sources.
Keep search terms simple. Do not overcomplicate a search with unnecessary search terms. Keeping the search terms more basic yields more precision. For example, do not search for "Haydn's Trumpet Concerto in E-Flat." Instead conduct an advanced search using terms individually: "Haydn," "trumpet," and "concerto."
Keep in mind that the composer of a piece of music is the author when searching the catalog. The example above would be best searched this way:
This is a simple advanced search that keeps the terms in the search bar basic, specifies Haydn as the author, and includes the terms "trumpet" and "concerto."
Also keep in mind that there is the ability to refine a search after the fact using the limiters that are toward the bottom left of any search results page. Especially take note of format, which allows the ability to refine the results to "music scores," and location, which allows the ability to refine location to "music library":