Get your lead edge stuck down nice and straight. This is probably the most important step. If this isn't 100% then it'll bunch up for sure. When sheet laminating, especially if it's using media from the tail end of a roll that has a lot of curl in it, it's best to let the media and laminate sit for awhile so they both lay flat. Stick a piece of coro over top or something to help flatten it out.
Then get your lead edge just started in the rollers. Now fold the laminate over the last roller before the media and let it drape over the back (exit side) of the laminator. I thread my laminate between a couple of rods on my laminator so when I pull slightly on the laminate it applies the tension directly on the last roller and not some other miscellaneous rod. Your laminator may be different than mine so I'm not sure what you're up against.
Now you should be able stand on the exit side of the laminator where you can apply a little tension to the sheet of laminate as it's fed through and you're pulling away the backing paper. It doesn't take much though, be careful not to pull hard enough to stretch it out and cause bunching.
Wider prints can be very difficult to sheet laminate with cast. A little extra media at the lead edge before you hit the printed surface will help prevent some mistakes. I find the thin cast lams can bunch up slightly in the first few inches and then sort them themselves out for the rest of the feed. 4-6" is usually enough. You'll see what I mean after doing it a few times.
