I dont think puting your arms to the side and pushing up is an option when someone sinks a guillitine choke on you. Aside from a rear naked choke, when applied properly, the guillitine is one of the more controlled and easy chokes to apply, and one of the hardest to escape. Of course we could say what to do if you catch someone whos going to apply it, but once your in the guillitine its a different story. Someone above replied and you need to tuck your chin as much as possible, which is the basics of protecting your self from the choke. When "practice grappling," me and my associates usually just tap when a guillitine choke is applied properly to avoid damaging eachother.