My grandmother is the golden example that I try to emulate.  Her son, my dad, was killed on WW2.  That left my young mother with a little baby, me.  My GM treated my mother like a daughter.  We stayed with them for months at a time.  

When my mom decided to remarry, she discussed it with my GPs.  They told her they realized I needed a father in my life and gave their blessing.  They even attended the wedding.  My new dad had a somewhat difficult personality but they welcomed him like a new son-in-law.  She made him so welcome that we travelled there at least twice a year and always at Thanksgiving  I can remember her saying sincerely, "Oh, NewSonInLaw, you're so funny" when he made a lame joke.  She laid on the hospitality.

When Mom had 3 more children, they automatically became her new GKs.  Of course, I thought all this was normal and didn't realize til older how exceptional she was as a MIL.

My first MIL and I got on fine. She spoke very little English and I spoke and understood even less of her native language. If she had complaints and shared them with her son, he never told me.

My second MIL had a contentious relationship with the ex wife. My view, and from what I have gleaned from conversations with various relatives, is that there was fault on both sides. MIL was always gracious to me, and I to her. She did not want a repeat.

Both are gone now. I miss having both in my life.

DH's mother passed several years before we met, but I've heard nothing but fantastic things about her from multiple family members so it's sad we didn't get to meet.

My former MIL and I (my ex's mother) got along really well. The only two issues she had were that we didn't get married in a Catholic church and I didn't want kids (neither did he). She eventually got over both of those and was lots of fun to hang out with and do things with.  A little neurotic maybe but she had a difficult childhood and adolescense that shaped who she was. I was sad that she didn't want to keep in touch after the divorce, but she had loyalty to her son which I understand.

She was 97 when she passed last year, right before COVID hit. She was very old, when I started my relationship with Husband, so while she was very sweet and kind, she was a bit distant and not very active in a relationship with me. We did some caregiving of her odd weekends. I made her tea.

And then, she would forget that Husband was divorced and when a birthday or Christmas came around, she would ask one of the skids "you should invite your mother, Im having a big birthday party!" She wasnt super out of it, just very vague. Thats the only thing that bothered me about MIL was her being very open to having the Toxic Troll over to family gatherings.

MILs should butt out and not listen to either their child or the child's spouse talk bad about the other.

This ^^^

My DH's mother died before we met, but one thing that DH told me that stands out, is that she never wanted to hear him bad mouth his first wife. She said that he would forgive her (for whatever was going on), but she would not and would always have a bad taste in her mouth about her, so although she wanted to be supportive of him, she didn't want to hear about their serious disagreements and problems.

EX DH's mom wrote the book on how not to MIL. She favored my ex's younger sister and her kids in a way that was obvious and alienating. She was cold and never offered a kind word.  I remember when we told her we were expecting the only thing she said was don't expect me to babysit.  Ummmm wasn't gonna ask!  My ex was always the odd kid out, even now I feel bad for how his parents treated him.  It played a big role in the type of spouse and parent he was.

My DHs mom was the exact opposite.  Kind, welcoming and treated al the kids and grandkids equally.  She was a lovely lady.  

I will add that my own mom was and is a good MIL.  Doesn't interfere, helps when asked and never criticizes parenting.  I learned a lot  from her. I never ever criticize how my kids parent. I follow their rules in terms of how they parent their kids.  I've told both mine I raised you you raise yours.  I bend over backwards to be flexible abt holidays--i absolutely will not demand attendance on any holiday.  I love my kids and their spouses.  I try to be helpful but not intrusive.  It's hard at t8mes but parent8ng is different today and I really think each generation has to find it's own way in this area.

My first MIL lived in another country, so for the most part was not an issue intervening.  She did have a strong opinion on my divorcing her son even though she first hand witnessed him strangling me when she made a visit.  

My current MIL we've had a lot of ups and downs. She' not overbearing but we disagree on a lot.  She tends to coddle her sons and see all women in their lives as mortal enemies.  She'd rather have them both living with her the rest of her life.  My BIL does already.  

My MIL knew no boundaries until me.  She would walk in uninvited, show up uninvited, try to invite other people to our house for get togethers.  Luckily those people had the good sense not to show.  When I had my daughter, she tried to completely take over.  She wanted to be the mother, and I guess I needed to stick around in case she wanted me to watch "her" baby.  She did the same to dh's sister.  She did completely take over her kids because SIL let her.  I wasn't so easily pushed out of the way.  Only mistake we made was letting her babysit my daughter when we worked.  She did whatever she wanted even if we felt it was unsafe.   My husband got a better paying job, I quit mine, never let her babysit again. I had my son after I left my job.   We set hard boundaries with her, which caused some hard feelings between us and other family members.  MIL cried to whoever would listen about we wouldn't let her see the kids.  Not true.  We just didn't let her do whatever she wanted.  And that is how NOT to be a good MIL.  

My only real annoyances with MIL stem from her criticism or interference with my parenting. Sometimes it's sneaky stuff like talking to DD about religion when she knows that we don't want DD to have anything to do with her version of Christianity. Other times she flat out tells me that something I'm doing with DD is wrong and I should change it. In either type of situation I end up feeling very frustrated. Other than parenting stuff, we really are very close and I love her. I just wish she could bite her tongue when it comes to DD, but it seems that she is literally incapable of stopping herself. 

I've been really lucky with my MIL. She and FIL live a few hours away so we don't see them often. They always plan visits in advance and never overstay their welcome. I never get advice unless I ask for it. DD adores them and I reckon she's their favourite grandchild. They're just stereotypical honest old farming folk that grew up during the depression. They're penny pinchers but on themselves most of all. It drives DH insane sometimes how they won't spend a bit more but that generation went through some tough times that clearly still affect them to this day. My mother is the same and she grew up starving through a civil war so MIL's behaviour isn't out of the ordinary for me. 

The best bit was when DH was going through his period of arseholeyness both MIL and FIL said they'd completely understand if I chose to leave DH and they'd stand by and support me. Said maybe something drastic might just be what DH needs to pull his head out from his arse!

But she is very passremarkable.  Meaning she likes to pass snide little remarks.  ie Why does TASM have more closet space than Mr TASM?  Or boarderline rasist remarks about my country of origin.  Or comments on how we spend money.  Or my oven gloves.  Or the pillows in the guest room.  etc, etc, etc

When she would come to visit, DH would leave her with me and go off doing his projects.  After a couple of times, DH and I had a come to jesus session where I explained that MIL is just like a skid.  Visitation is with the blood relative not with TASM! Luckily, DH is a quick learner.

I swear I hit the jackpot with MIL's! 

I think the biggest thing is that she always takes my feelings and opinions seriously. She never plans without talking to me. She is just so kind to me and my kids.