A legal expert sent us an email and asked that we post a short article on this topic to help out people representing themselves. These are things that lawyers learn early and it's easy to overlook that everyone might not know them.
As is discussed in our ebook, The Guerrilla Guide to Legal Research: Finding the Law for Non-Lawyers, it is important that you not only find the case law that applies to your case but also that you understand why it applies and further, that you understand why other case law might not apply to your case.
Unfortunately, there is no way we could explain in an article, or even a book, everything you need to know about reading and understanding cases since that is something that takes three years of law school and then is an ongoing skill you continue to develop throughout your career as a lawyer or legal scholar.
But there are a few things we can tell you that are particularly important.
First, make sure the case you are reading hasn't been overruled or interpreted by some later case. This is done by "Shepardizing" a case (this is shorthand for using a particular publication produced by West Publishing) but you can do this by just looking at a list of the other cases citing this case. All legal search engines, including Google Advanced Scholar, have an easy way of doing this, just poke around on whichever one you use and you will find it. Then, read all the cases in which the case you intend to rely has been cited.
Second, when you read a case, be sure you know what part of the case you are finding the language you like. If it is in the majority opinion, then it is "authoritative" and courts should follow it. If it is in the concurring opinion (that judge agreed with the majority but wanted to make certain points that were different) it is not authoritative but it might be considered persuasive, and you may be able to use the same argument and get the judge to agree with you but be sure that you let them know it is in the concurring opinion. If it is a dissenting opinion (the judge disagreed with the majority) then it really has no weight at all and while you can cite it, the judge in your case has absolutely no reason to accept it as authority.
Third, as a general rule Court of Appeals rulings in criminal cases don't apply, or apply in a very limited manner, in civil cases and vice versa. It's not at all unusual to see a "natural law" proponent ranting about language as to rights not being properly applied without realizing the case from which the langauge was taken was a criminal case and he/they are now trying to apply it in a civil case. The explanation of why this maxim is true would take more time and room than we have here but it is almost always true and the exceptions are few and not likely to be of any help unless you have a thorough background in legal theory and history. Just remember, criminal case law for criminal cases, civil case law for civil cases.
Finally, remember, 1) the higher the court, the more authority it carries, and 2) the more recent cases are better than older cases when citing for authority.
Of course, these aren't everything you need to know when interpreting case law but they are certainly some of the more important things.