How to Address Your Mother-in-law
Step1
It's possible you've gotten through the entire courtship and dating process without having to call her anything at all. Maybe you've never even met her. The very best time to figure out how to address your mother-in-law is before your first, face-to-face meeting. If possible, get your spouse's advice; he or she might have insider tips (such as, "Her name is Agnes, but her friends all call her Bunny').
Step2
Start with the middle-ground, given first name. Depending on your age and the culture you were raised in, it might seem awkward to address someone your parents' age as "Betty." But that's the best place to start. Few people will object to being called by their first name. Start with a question: 'May I call you Betty?" If you get anything other than an enthusiastic response ("Of course!" or "For heaven's sake, call me Poopsie!") go on to the next step.
Step3
The very next time you have the opportunity, address your mother-in-law by her formal title ("Mrs. Lewandowski"). She might well respond with, "Please, call me _____." If so, you're home free. But remember, she may have no idea what she wants you to call her, especially if you're the first offspring-in-law in the family.
Step4
If "Mrs. Something" feels too stiff to both of you, yet neither of you is comfortable with the "just-buddies" feel of calling her Lois, Martha, or--heaven forbid--Binky, compromise with "Mrs. First-Initial-of-Last-Name." This works especially well if it's a difficult last name, because your spouse's young friends probably called her that. If you're a woman and you've taken your new husband's last name, you can also refer to yourself that way: "We're both Mrs. First-Initial-of-Last-Name now!"
Step5
A respectful variation in some cultures can be "Mother Grabanczyk" or even, "Mother G." Having children might resolve the whole issue, because they will naturally come up with a name or nickname for each grandparent. You can help them shorten "Your Montana grandmother" into "TanaGram," but they're likely to call one grandmother "Oooma" or "Nana" anyway.
Step6
When you've really been accepted into the family, she might ask you to call her "Mom"--but if that never happens, don't be upset. It might seem weird to her to be called "Mom" by someone she didn't give birth to. Use "Mom" only if it's comfortable to you both.