It's a good idea to restrict your presentations to being about 18 to 20 minutes long, Carmine Gallo writes. Using this as a constraint might allow you to hold your audience's attention and lead to a better overall presentation, he notes. "As a communications specialist, I've learned that a 'constrained' presentation is often more inspiring, creative, and engaging than longer, unbridled presentations that are boring, confusing, and convoluted," he writes.