You need to put your glasses on after you don the respirator.
I don't think it matters which strap you fasten first, as long you do a seal check and it's tight enough so it stays sealed even when you move your head around and bend over.
Here's a scene from Andromeda, which I posted before...
Also, your glasses don't fog up when you're wearing a respirator, like they do when you wear a cloth mask or a loose-fitting earloop mask. But sometimes a filtering facepiece respirator will fog up glassses even if you have it on tight because the exhalation breath comes out from everywhere through the filtering material, even near your glasses.
glad fuckers like you are getting vasectomies