Typically based on their personality or ability. In my case, I chose my name based on my ability- well, the ability I had before I arrived here.

[He leans back slightly, arms folded across his chest. Soundwave isn't his original name, however, being an amnesiac without any recollection of what his past life was. But at this point, what or whoever he was doesn't matter anymore.]

Although, 'Soundwave' is the closest translation for the human tongue, as Cybertronian language is unpronounceable for organic species.