The simple fact that your asking this questions, means you and your wife will make excellent grandparents! All you need to do is care, the rest will fall into place.
I used to spend a couple weeks each summer with my grandparents in NH, and would go up every other weekend with my uncle to visit them. My grandfather never really knew what to do with me, he was funny that way, but I liked to play mini golf and eat ice cream, so sure enough, every single time I went there, he would take me mini golfing and buy me ice cream. I had a blast because he was doing something with me that I liked, and he didn't worry much about anything besides making sure I had fun.
My most lasting memory of my grandfather, was at that same golf course (it's still there today). He went to the counter to pay for the two of us, the price had gone up since the year before (I don't know how much, probably a dollar or something). He looked at me with a look of disgust and disappointment, he said "Matt, there's two kinds of people in this world, the SCREWERS, and the SCREWEES, you don't want o be the screwee".
I was probably 7 or 8 years old at that point. I've never forgotten my grandfathers "words of wisdom."
He lived alone on that mountain in nh for a long time. He stayed in that house through some pretty bad winters and took care of himself. I watched him pass this last winter, he finally gave in the day before his 96th birthday.
He left a very lasting impression on me, and I have so many memories of him.....all because he simply just plain CARED.