The more stuff that is on a page or some piece of instructional material, the higher, the cognitive load. So try to only put on there what is necessary for the learner. Because remember, the learner cannot distinguish what is important like an expert can. Related, try not to have something, both in written form and in spoken form. That increases cognitive load, which makes it harder for the learner to understand because they are trying to contrast and meld the two together.