Oh heck, thats easy. First you take a very real problem like... global warming for example. Then you pay a cabal of associates to pass themselves off as scientists and experts to denounce it as a foreign lie. Then you convince everyone that you are surrounded by those out to threaten your very way of life, be it foreign powers or homegrown liberal secular homosexual elite, and even though the arctic ice is melting at a rate of knots, it's all wicked foreign lies. You let that simmer for a few years, all the while continuing to stoke up fear and paranoia and after a while nobody will even care what the truth is. As the saying goes, tell a lie often enough and it takes on a truth of its own. Finally, when panic levels have hit fever pitch, you tell everyone you alone can protect the Homeland, all they have to do is follow you. Then they will give up their freedom willingly and you can do whatever you want to them. Of course, there will be few dissenters and non-believers. At first you will discredit them by questioning their patriotism. Your cabal of associates will be helpful here. Then once you have most of the people following you they will shout down dissenters themselves. Once you have the power, you just kill them.
Wasn't that easy?