Definitely focus on a specific era if you want to learn history to an academic level of detail. Even people who spend their lives studying history would be hard-pressed to know about all areas of history. So I would first pick an area that you think will interest you (e.g. Roman history), and read a general history of that area. After that, you can read more specific books that elaborate upon whatever you found most interesting within that broad topic (e.g. the Late Roman Republic, Roman religion).

I wouldn't worry too much about the authors, if you're just introducing yourself to an area of history then almost all historians will do a good job of giving an outline of a period. I'd say that later on is when you should start worrying about different historical debates. To start, just have fun learning about something new:)