BARdiver,
A mask squeeze should not occur to a diver these days. To have it happen means some very basic things did not occur--equilizing the mask's pressure. It's like equalizing your ears, only a different air space. The divers above have pretty well explained what needs to happen, equilize early (starting just under the surface), blow out your nose to ensure that the mask equilizes, etc.
But I want to elaborate a bit on mask fit, because it can influence whether the mask equilizes well. The type of mask is also important. Let me elaborate--the mask needs to fit well, and as stated above it should fit without tightening the mask strap. Actually, you should be able to keep the mask on your face with only suction pressure from an inhalation. If the mask falls off, without the mask strap, then it doesn't fit. I currently have a number of masks, some "vintage" and some modern. I picked up a mask I loved off E-bay, a Farralon mask with three windows, that I had in the 1980s. It has a nose pocket, and is a close-fitting mask, so I really liked it. My old mask was messed up when my LDS put a purge valve on it in the skirt, not the nose pocket. So I was really happy to receive it from E-bay; that only lasted until I put it on, and it would not seal. Over the years, the rubber had stiffened a bit, and no longer fits my face. I have not had it in the water yet, and won't until the rubber returns to its original shape, if it ever does. The fit is critical, and may influence whether you get a mask squeeze. If it is too tight, and comletely seals around your nose (completely encloses the nose), then it is possible to think you've equilize when only the nose pocket is equilized. I don't know of this ever happening, but it is a possibility with the newer, close-fitting styles of masks. In this case, while equilizing the nose pocket, the eyes will still be unequilized and could cause an eye squeeze.
Good luck,
SeaRat