Ignore social media etiquette: While many grandparents aren't plugged in on Facebook and Instagram, it's important for the tech-savvy few to abide by some unwritten social media rules: don't post unflattering/inappropriate photos of the grandkids, don't hijack every post and turn it into a conversation, don't make vague statuses to guilt kids or grandkids, and don't add your grandkids' friends unless they instigate it.
Suggest baby names: Choosing a name is a very personal experience for parents, and hearing others' unwarranted opinions is very difficult. No future parents want to know that Edith was your elementary-school bully or that they should name their baby after a distant deceased aunt.
Buy major gifts without consulting the parents: Whether it's a car, a life-size teddy bear, or an iPad, grandparents should never make major purchases for grandkids without consulting their parents.
Expect to be present in the delivery room: Whether a new mom invites her parents or in-laws into the delivery room is her choice, and being pressured either way is not helpful for anybody.
Force beliefs on the grandkids: While you might think that it's important to raise them "the right way," you should allow children to determine political and spiritual beliefs on their own.
Leave parents out of the loop: There's nothing more frustrating than not knowing your kids' whereabouts — even though grandparents are usually trustworthy, it's extremely important to keep Mom and Dad in the loop.