Tradionally we like promos to be used that are set in the square and released by BBC themselves.
We also prefer for solo promos to be used rather than ones where the character is in a group although if the character has no other promos we do allow exceptions to be made.
We also don't use promos that are for the actors themselves and not the characters which was the problem that Walford E20 is referring to. It is hard to tell the difference sometimes so if your unsure reach out to me and I'll help.
Studio promos are a massive no no, only time we allow them is if the character has no previous promos as we do prefer them to screenshots.