I have been doing genealogy for about 30 years and am active on Ancestry.
Ancestry works well in the US, not much elsewhere. Also you can use FamilySearch, the LDS church system, for free. Also, there are free databases about the immigration of everyone who came in through Ellis Island and its predecessor Castle Garden.
An item that came onto Ancestry and FamilySearch just a few years ago is SF funeral home records.
There are free digitalized California newspapers including some years of the San Francisco Call. I even found a cartoon about a great-uncle.
One thing Ancestry cannot replace is the memories of older people. You need to speak with them before their memories are lost. For example, my oldest cousin is 99 and still recalls my grandparent who died in 1922.
My own earliest memories are probably from when I was 2, when we moved from Fell St. to the Sunset.