Delete the decoration from your slides

Working memory is the bottleneck all instruction squeezes through (Sweller, 1988), and the multimedia research is blunt about what helps: removing interesting-but-irrelevant material improves learning, an effect strong enough that Mayer (2009) lists coherence first among his design principles. The decoration isn't neutral filler; it competes with the content for the same limited channel. (Manning's cognitive-load-analyser skill audits materials for exactly this.)

In practice

• One idea per slide, words or image doing work, nothing else. If it doesn't help the explanation, it taxes it.
• Don't read paragraphs off the slide while students read them too: same channel, twice the traffic. Speak to a sparse slide instead.
• Save the fun for transitions and starters where nothing competes with it. Humour has a place; mid-explanation isn't it.