Something I bump into every now and again that I really should’ve written down before. Let’s say you sometimes work with multiple monitors, you then switch to a single monitor and launch an application, but it loads up on a monitor that’s no longer there – it’s hidden away, tucked off screen with no way to drag it onto your actual monitor.
Press Alt + Space bar, it’ll pop up the window manager prompt for that application on the edge of your active monitor, from there you can click Maximise and bam that window now appears on the active display. From here you can resize at will.