Keyword Searching
Keyword searching, using terms you, as a user, are familiar with, is the usual first approach to any database. This is called searching using natural language. Searching by keyword will always return something of use to the user. In this regard, the search is rewarding. However, keyword searching, generally returns more references to articles than one can actually manage to review for their relevance. 
A successful search should return 25-30 references. The specificity of scientific terms may mean that keyword searching find you exactly what you are looking for--or, maybe not. A good approach is to look at a few of the references to see if they are what you are looking for. If they are, then examine the subject headings for the record and search according to subject heading (see below) OR combine your keyword search with a field search (see below) to narrow your results. Both strategies will increase the specificity of your search.
Subject Searching
Subject searching is a form of searching using a controlled vocabulary where a limited number of of pre-defined terms are assigned to the reference based on an analysis of the content of the article being indexed. When you find the correct subject heading, the search returns fewer but definitely relevant articles regardless of whether they contain particular key words.
PubMed uses MeSH as its controlled vocabulary. MeSH stands for Medical Subject Headings. The MeSH headings applied to the Wilson & McNaugton (1994) example paper appear to the right.
To learn more about searching using MeSH headings, check out this video tutorial from the folks at NLM.
Field Searching
Field searching allows you to search specific fields within the citation. A list of fields that can be searched appear to the right.
Field searching is available through the Advanced Search function of PubMed. To search specific fields, use the pull down menu in Advanced Search search-builder and then enter your search term. If you already know the fields you wish to search, you can enter them directly into the search box. Examples of field searching include:
tatsuno[Author] --- to search all articles authored by Tatsuno.
or
tatsuno, masami[Author] --- to search all articles authored specifically by Masami Tatsuno
or
lethbridge[Affiliation] -- to search for articles where the authors were affiliated with the University of Lethbridge at the time of publication.
or
Neurons/physiology[Mesh] -- to find articles that discuss the physiology of neurons as categorized by the MeSH.
Using Boolean Operators: AND, OR, and NOT
Boolean operators can be used in the Advanced Search option of PubMed as part of the Search Builder.
Truncation and Wildcards
Truncation and wildcards are not available in PubMed.
Limiters
Once you have retrieved a list of references, you may want to refine the search by limiters or facets or, as they are known in PubMed, filters. Examples of PubMed filters include article type, publication dates, species studied, etc.
These filters can be pre-set by using the Manage Filters function through your MyNCBI account.