If there are ever any lights glowing in the 707, I quickly to look them up in the ‘707 Captain’ FLIGHT MANUAL Part II – Aircraft and Systems (cs707_manual2.pdf), to find out why they are ON, how to get them OFF and what will happen if I don't get them to go out.
This is a good way to learn about an aircraft (not just the 707). The same applies to all the manuals dealing with it. If I'm trying to do something I can't figure out, out come the manuals an I start looking for help with what I need to know.
I read up on how to start the aircraft and then I go for a flight. I look into the manuals after I have flown around for a while in the aircraft. This is the case for all my third party aircraft, except one.

With the 707 engine start, I kept at it until I came up with a way to get them started every time I tried. Once I could get them started every time, it was time to learn the rest of the procedures and about the instruments.

Mark