Cover Up question

Hello all,
Someone is asking me for a cover up and then I realized, I had no idea how or if there are certain mechanics in doing cover ups.
So I am here to ask, are there tips or best practices for cover ups? I would believe it is not just slap a bigger darker image on top.
The existing image is just a set of roman numerals forming a "once significant" date for the person.
Thank you in advance for all replies.
Kind regards,
Ed

Do you have a picture of the tattoo you've been asked to cover?

I did 2 covers, one i totally covered with a new tattoo, the other i somehow upgraded the original design.

Peace,

DKJ