You need enough text to help the art tell the story, but if it'll clutter up the art, you'll need to cut it down a bit. The story comes first, so if, for instance, if it's necessary to write a lot of dialogue, make sure the art leaves enough room per panel for more/bigger word balloons, and maybe add more panels to accommodate the whole conversation.
A little wordiness isn't a bad thing, and even though big splash panels with as few words as possible is the current big thing in American comics, it's worth knowing that wasn't always the case. The best writers of the Golden and Silver Age tended to be a lot wordier and still managed to tell whole stories in single issues, something not very many writers in traditional American comics do nowadays.