Write it so someone else can reproduce it without asking you anything. Bugzilla's filing guide asks for a specific summary and precise steps to reproduce, and common templates add the expected and actual results stated separately, whether you can reproduce it always, sometimes or never, and a clear split between observed facts and your speculation about the cause. Add the environment (build, OS, browser or device, account role), preconditions, evidence such as a screenshot, video or log, and severity with the user impact. Atlassian's template adds frequency and impact fields. Check for duplicates first and retest on the latest build.

Sources: Bugzilla: filing a bug, Atlassian Community template, BrowserStack guide