Firstly, insulting voters, whether basket of deplorable style, or the more Trumpian style attack on anyone who crosses you at the moment. Hold them in contempt, if you like, but have the wit to keep your mouth shut even if your true believers lap it up.
Second, insulting the voters’ intelligence by uttering ridiculous promises. Building a wall that Mexico will pay for, or sending everybody’s kids to college and sending Jeff Bezos the bill. And don’t compound the error by telling the voters they don’t comprehend their own interests.
Finally, I would say openly lusting for the power to bring low your designated enemies, whether they are rapacious border-crashers or wicked billionaires. It plays well with the zealots, but people of sense pick up a whiff of authoritarianism from that. Not the crazed folks who see Nazis behind every tree, but the ones who prefer an unedited version of the Bill of Rights.