It's not easy. IGFS is quite stiff and doesn't go easily in to the rear maual sheet feeder. And it's too thick and stiff for paper tray. If you use the rear feed and the printer tells you it's not straight, you can slightly lift the lever that locks the paper feed rolls and then align the paper while watching through the top cover. Then just push tha pause button once. This method sometimes screws the margins however and it's wise to leave enough area unprinted that you can trim the margins if needed.
The front manual feed needs a bit more deskspace behind the printer but doesn't bend the paper unlike the rearfeed does.
Anyway it's interesting to note that a "professional" printer like this is sometimes a source of frustration with both this kind of paper handling problems and also with potential clogging issues and at the same time, a 100,-$ Canon desktop inkjet has performed flawlesly for 6 years now and nothing in the world is easier than feeding any paper that this machine accepts. And no clogs... Ever.
Cheers,
J