In genealogy (or any other) research: Document your sources as you go.
I find a lot of contradictory information like, my grandmother is reportedly older than her mother, and I see that a headstone is the source of Gran’s birthday and her mother’s source was a drunk uncle.
I create a source called Family Stories and link it to all unverified information that I remember or am casually told at family events. I link that to events like births, marriages, divorces, deaths, immigration and adventures. I can tell at a glance when a new source is more/less reliable. Items linked to the Family Stories source is also a checklist for research for better sources (e.g. Newspaper obituaries, Registers of Births, Deaths and Marriages, military service records).
Interviews with family members get their own separate Source record. Even if I didn’t record the interview and only took written notes – that’s a source. I try to record all interviews, but sometimes that isn’t possible.
Always put the URL of any website as a source where you found something or someone. Later on you’ll want to check something again and the URL will be right there. I missed doing that a couple of times and it took ages to find the data again via my bookmarks and other notes. I eventually had to use Google again and wasted about two hours.
Get a copy, printout, recording or photograph of all sources where possible. I then copy or scan it to my media folder and note its location in the source record. You don’t want to go to a library a second time just to confirm spelling of a middle name on newspaper microfilm archives.