You could yawn first? Or just stare at something for a very long time until your eyes start getting itchy and watery, or umm think of someones death or anything else really sad... Hope this sort of helped!:)
What I do, think of something really bad that happened to you, like I think of my maw maw dying, then kinda like push ur eyes together (like blinking) if that makes any sense lol, then you should be crying :) good luck!
Would it be cheating to use eye drops or onions? Use "Method Acting" - the use of summoning up personal past experiences to incorporate in the portrayal of your character. Holding your breathe long enough to make your face red might also bring some tears. It is said that Meryl Streep played with her character's children right before she had to *Spoiler Alert! * send one of them to their death in the denouement scene in the film "Sophie's Choice". She also hugged a block of ice for 15 minutes prior to being "dead" in "Ironweed". Could you pinch yourself hard enough to bring tears to your eyes? It wouldn't be the first time someone "suffered for their Art" ...
Squeeze your eyes shut tight and your tear ducts will "burst" releasing fluid (tears). I went to an acting school and depending on the scene different methods were used, but when you're in character, if you can't find yourself willing to cry, then this was a go to move. you can tilt your head down and pretend to stifle back tears if you dont want this to be seen as you do it. the more you practice the easier and more natural it wil look
Remember all the bad things that occurred in your life before, and I mean REALLY REALLY BAD things, my friend, who fake cried when he got in trouble, told me that it was a mere, "Memory of all the terrible things in my life".