My dad took the time to learn about current advice so I felt really supported when I was getting to grips with breast feeding. He knew all about feeding on demands and the steps for getting a good latch. He also knew about safe sleeping advice, later weaning and as I wanted to baby wear ticks. Mil knew nothing about current advice and would try to put dd down on her front.
Give baby back to mum or dad as soon as they cry. Don't rock a jaundice baby back of to sleep when mum wants to feed them.
Keep visits short. The worst experience I had was sandwiched between two relitives with one of them clutching dd when all I wanted to do was sleep. They stayed for hours including through midwife's home visit.
Ask if new parents want you to let anyone know about baby's arrival. My dad announced on facebook when he knew dd had arrived safely with our permission. My mum had a list of people to phone around.
Take pictures of the new family and don't insist new parents take lots of posed pictures of you with baby.
Texting to see if anything is needed before a visit. Or if you're in a shop.
Let them know when or if you are avaliable for support. My mum held both our newborns in the small hours when dh and I were exhausted. She was clear we could call her any time of the day or night.
Doing washing and drying was the most helpful thing ever.
If it's your dd my mum was around to help with more personal care post birth like removing residue from dressings.
Have things at your house but don't make them for when you have baby just to make visits easier. My mil tried to kit out a nursery and wanted a posh pushchair so she could do the shopping when she had the baby. My mum borrowed a bouncer and brought a changing mat for us to use when we went over and said pop over if we needed a change of sensory any time.