Co-first authors are traditionally denoted with an asterisk, and the order of the persons is determined by the PI. When the work is published, the authors' names appear in print as "co-Author 1*, co-Author 2*, Author 3, and Author 4." If one or more of the authors is/are married, his/her spouse(s) may be included among the authors.
If there are more than four authors, they are listed in alphabetical order. Authors who have contributed equally to the work should be listed in alphabetical order, followed by authors who have not contributed equally. If a single author writes several papers that are published simultaneously or within a short period of time, he or she can list each paper individually under the byline system. In this case, it does not matter in what order the authors are listed.
Authors who have not contributed equally to the work can be listed in three ways: by title, by contribution, or by order of appearance. By title means that authors are listed according to which part of the work they contributed most significantly to. For example, an author who did the background research for a publication can be listed as the "title" author. By contribution means that authors are listed according to how much they contributed to the specific part of the work. For example, an author who performed all the experiments related to one figure could be listed as the "contribution" author for that figure.
Yes, the first author is listed first, followed by the second, and so on. Typically, the first author performed the bulk of the work (in terms of data contributions—they are also generally the person who produced the article, at least where I work), the second author did the second most, and so on. Some articles have more than two authors; sometimes this is the case for an article that is not considered to be an original research publication.
In most cases, the order of the authors' names is based on their contribution to the study. If there are multiple groups working on an article, each group may be given a letter designating their status as first author, co-author, etc. Then the names of these individuals would be listed in order based on which group they belong to.
However, some journals have policies regarding the ordering of authors' names, so if your journal has such a policy you should follow it.
Also note that certain roles can be played by more than one author. For example, an article can be written by a team of researchers rather than just one author. In this case, all authors who meet criteria set by the journal (for example, being named on the paper) will appear on the paper. They do not need to be ordered by name, but they must all be identified so that others can verify their contribution.
When a book has two authors, arrange them in the same order as they appear in the book. Begin by listing the first author name that occurs in the book in last name, first name format; following author names appear in alphabetical order (first name, last name format). For example, if the first author's name is "John Smith" and the second author's name is "Mary Johnson," their entry would look like this: John Smith and Mary Johnson.
It is up to the editors to decide how closely to follow this rule. Some publishers may require that authors be listed in order of appearance, while others may allow for some flexibility. However, as a general rule, if the book has more than one author, list them in order of appearance.
This rule applies even if the authors have the same first name or last name. For example, if the first author's name is "John Smith" and the third author's name is "Jane Doe," their entry would still be "John Smith and Jane Doe."
If there are multiple authors with the same first name or last name, such as "John Smith," it can get confusing which one to list first. Use your best judgment based on information about the authors provided by the editor. For example, if one author is given a title or a chapter designation before another author, list him or her first.