Look really closely at a couple things: hands and any broken lines that should be straight.

Hands hopefully is obvious. AI has trouble drawing fingers. For the broken lines, picture a wall or a swimming pool or something that you know is a straight line, but is behind the subject. If the lines don’t line up, that’s a good clue.

Look at thin lines (hair, eyelashes, powerlines). In AI pictures, some lines just melt away and are not continuous. It’s a dead giveaway

Look closely at the little things in places where you expect to see “things” and see if they are actually the things you expect them to be. With AI they often aren’t actually things at all. Also patterns may look right until you examine them closely.

Collective human wisdom would be useful. Some humans will pick up nuances and details other humans may have missed. Sort of complementing each other, in a way.