This post serves as a reminder to my self. May I return to it in 30-odd years and find that I've lived up to it. If not, may this post embarrass me and make me change my ways.
To love your children means to respect them. To respect them, means to accept their choices without comment. You may not always agree with the choices you make, but that is rather irrelevant. Although we may see children as little horcruxes, you have to let that piece of you live it's own life.
No matter what choice your children (or anyone else for that matter) make, it is theirs to make. And under no circumstances do you have the right to do things differently in their house. For example, if they use a dishwasher to wash and dry their dishes, and really prefer to do their dishes that way, you have no right to sneak into the kitchen early in the morning to quickly do the dishes by hand, and put them away before everyone gets up. It doesn't matter that you think using a dishwasher is wasteful, and for purposes of this discussion, it doesn't matter who is right. If you are asked to do thing their way or not at all, the right thing to do is to respect their wishes. No matter how much you think you're trying to help them, you're not helping by doing things differently than they are used to.
If their house is a mess, you can only clean it up if you are specifically asked to help out, or if you offer to help, AND the offer is accepted. If they say: "no thanks" they mean: "No, thank you for the offer, but we either prefer to live in the mess, or we prefer to clean it up ourselves. At any rate, if you clean it up I may never find my stuff again. No, thanks." This does not mean you're useless as a parent or grandparent. It just means that cleaning up is not what is expected of you at this point in time.
It might also not be appreciated if you tell them over and over again, how you do all your laundry by hand. It's not really fair to compare a single-and-retired-person household with one with three kids where both parents work full-time. But again, that's besides the point. If your children want to use a clothes washer for every piece of clothing they own, that's ok.
This is not to say we cannot have useful conversations about anything. There are ways of talking about things, and giving opinions, without being critical. And when you've giving your opinion, and your children find it a useful suggestion they will incorporate it into their lives. There is really no need to mention it ten more times to indicate that your way really is the best way. If your children do not change their ways, even after you have enlightened them about the best way, it doesn't mean they don't love you or like you.
The trick to getting along with your children is to treat them like you would any other adult. With respect, and this respect will likely be returned. Add a dose of true caring and love, and you can hardly go wrong. You can have intelligent discussions, and joyful reunions without strain. Isn't that the kind of environment you would want to see your grandchildren in, and the kind of example you want to set for them?