Which family to start with? This is a tough one & I think everyone has their own answer.
I started with the family
I remembered, which was my mother's side. It turned out that there was already quite a bit out there on that one. By the time I finally found something on my father's side, I missed out on a couple of unknown relatives that were local who might have helped.
I've never focused on a single person or line. As soon as I hit a brick wall on one person, I move on to another. Very erratic, but I tend to be compulsive in other areas of my life - so I guess this is some sort of balance for me.
I understand the lack of info problem. My paternal grandfather died when I was 5 & his wife rarely spoke of him, so I had few personal stories to work with. HIS father had died before my father was born.
No one talked about him. My mother & older sister was convinced it was because he was an evil man.
I suggest you start with the people who are still living, who can answer questions for you. Although having them tell you stories may be better. I get much more info from elderly family when they tell stories & look at pictures. Example - my FIL has repeatedly told me he knew nothing about his grandparents - no dates, nothing! - until I found a picture of his wedding & there was his grandmother!
Good luck!