I had a great relationship with my mum until she died last year. Honestly, I don't think it's rocket science. Be nice!
My mum was extremely kind. Not just to me, but to everyone. She was just a genuinely caring person who would have done anything within her power to help anybody.
She was always ultra-supportive of what me and my sister did, and extremely interested. She asked questions and listened to the answers. But she never offered advice unless asked and there was never any judgement - she trusted us to find our own way through but was consistently there for support and encouragement if we needed her.
She was immensely proud of what we had each achieved and told us so often. She bitterly regretted that she had not had the same opportunities as we had enjoyed, but I never felt that there was any resentment for that nor any attempt to live vicariously through us - just genuine pride and pleasure to see how our lives unfolded.
As a grandmother, she was very hands on and involved, but again, in a very supportive way. She was fun and playful with the kids, and helpful towards us as parents. There was never any hint of pushiness or interference or judgment. She respected how we wanted to do things (even though dsis and I did approach things differently from each other) and she frequently told us both that she thought we were great parents. Her grandchildren absolutely adored her. So did my DH and my BIL, who she welcomed wholeheartedly into the family from the moments she first met them.
She was very thoughtful. She remembered special dates/events and often found little ways of showing that she cared, even when we were far apart. She always looked delighted to see us but she wasn't ever needy or demanding of our attention in any way. She never tried to guilt trip us about anything.
She had her faults, of course. And she got things wrong sometimes. But she always had the self awareness to be able to listen and reflect and apologise when she had got things wrong. And she never held grudges when we had got things wrong either... she was so quick to forgive.
I was never in any doubt about how much she loved me. Probably more than any other person on the planet could ever love me. She told me that often, and she made me feel it too. It was like she always saw the very best version of me that I could be, and she had absolute faith that that best version was the "real" me.
I miss her a lot, and I can only hope that I will be half as good a mum to my beautiful dd as she was to me.