Break up long monologs among several characters
There are some moments in some movies in which a long monolog by a single individual works well. Any inspiring public speech, for example, or when one character holds others transfixed with a tirade or diatribe. But movies are an action medium, and most of the time a long-winded dissertation by one character while the others simply stand and react gets boring very quickly.
To avoid this, take your longer speeches and distribute the material to one or more additional characters. It is far more interesting to see what everyone has to say on the issue, than to see what one person has to say.
Think about real life situations. Aside from presentations and reports in a business situation, or structured events such as a ceremony, no one thinks well of someone who hogs the conversation. Let you characters make their point, then let someone else have a turn. Good examples of this can be found in the original Howard Hawk’s production of “The Thing,” and also in “The Big Chill,” both of which have extensive exposition and opinion, but no one says more than a few lines at a time before another chimes in with his two cents’ worth.
The exceptions, of course, is when someone gets all wrapped up in his own rhetoric, as when an individual muses, reminisces, waxes poetic, or proclaims a higher truth with fire in his eyes. People don’t mind if a good storyteller talks forever. Look at the long pontifications of the characters in “Network.” But even these are handled as special moments, and the ebb and flow of normal conversation continues in between, serving both to break up the monotony, and also to uplift the long passages by contrast.