The simplest answer to the foregoing question is "Meeting all requirements." That said, here is a pretty common compendium of such requirements, some or all of which apply to nearly every known IT certification program:

One or more exams: With only a few exceptions, most certifications require taking at least one exam, but I know of no single credential that requires more than nine exams.

Educational background: Some certifications require a degree; others accept degrees in lieu of anywhere from two to four years of work experience.
Code of ethics: Many certifications require candidates to sign an agreement indicating that they will abide by a specific code of ethics as certified individuals.

Work experience: Many certifications require that candidates possess some number of years of relevant work experience (seldom less than one year, never more than nine years, across all the programs I have investigated). Many such programs accept college degrees or set numbers of hours of relevant classroom training in lieu of on-the-job experience.

Additional submissions: A smaller (but growing) number of certifications require candidates to submit projects, reports, or other forms of written work to become certified.

The preceding list of elements represents requirements that occur in the majority of IT certification programs. Other less-common requirements include completing formal application forms, getting endorsements or recommendations from current credential holders, submission of teaching videos, or completion of specific coursework.

Please note also that once obtained, the majority of certifications then impose recertification or maintenance requirements on their holders. Many programs have continuing-education requirements, whereby certified professionals must attend conferences, classes, or seminars to retain their credentials. Some simply require certified professionals to retest at regular intervals, whereas others require professionals to track updates to software or platform versions by updating their credentials within 12 to 18 months of new product releases. Whatever the specifics for some particular credential might be, you should expect to invest additional time, effort, and money in keeping IT certifications up-to-date once they have been earned.