If Trump claims a victory that is not rightly his, a few marches in the streets will not be an adequate response. There may have to be a sustained campaign of civic action, as in Hong Kong and Belarus, to rally the majority that wants to preserve democracy, that isolates those who would undo it.
David Brooks at the New York Times on what may need to be done if Trump attempts to claim victory before all the votes are counted.
If you can vote early then please do so. When you vote early in person at an early voting center then your vote is counted on the evening of Election Day. When you vote by mail your vote may not be counted for days or even weeks. If Trump is the clear loser by sunrise on November 4th then the country will be spared a lot of stupid Trump drama and chaos.
In the meantime, follow the news from Belarus to get an idea of the types of actions (like peaceful mass protests and strikes) which people have been engaged in since the rigged election of August 9th.