the “best way” is probably to hire someone (depending how you define “best”)
A great starting point is Jewishgen .com
I was able to put together a family tree going back 8 generations. However, Ihave an unusual last name which made it easier since it limited the number of hits to sift through. If you have a name like Stern you will need more starting information, as obviously the number of Sterns you will uncover will be overwhelming