1) Federal or State: do you need a docket for a federal or state case?
2) Time frame: older materials may not be available electronically
3) Filings: Do you just need the docket sheet, or do you also need to access the underlying filings?
Dockets basically are a summary of proceedings in a case. They provide a handy way of keeping track of what is happening (or what happened) in a particular case and can also lead a researcher to the documents that were filed in that case. A docket sheet will typically supply the names of the parties and attorneys, the docket number and the name of judge, and important dates(e.g., the date that the case was filed, when the last action occurred).
Most importantly, a docket will provide a list of actions that have occurred since the case was filed. For example, you could see when documents such as pleadings, motions, or briefs were filed or served. Some electronic dockets will also provide access to an electronic version, such as a PDF, of the actual filings. PACER, for example, usually supplies links to many of the documents that are referenced on a case's docket sheet. This guide will indicate when filings are available.