Good comments on the flat side of the needle and such. Thread always comes out the flat side of the needle is another way to look at it. Some machines thread front to back and others side to side. Often if you put a mirror under the needle holder you can see the direction of the flat side.
I'd be more concerned about how the thread gets from the spool to the needle. Many machines will have little icons with numbers or arrows on them to give you a clue. I'm pretty good at figuring out how thread various machines but my mother-in-law had one that was a real mystery and not intuitive.
Winding bobbins is another thing where machines differ on how to run the thread from the spool to the bobbin holder.
How the thread is wound on the spool can also affect things. It used to be all thread was "stacked" or wound round and round. Coats and Clark is still done this way. Those spools used to have a little notch in the edge to catch the thread when you were done with it. Thread wound this way is put on a vertical thread holder. Thread now also come wound in a criss cross fashion and you can see it clearly when you look at the thread. Gutermann, Mettler and others are wound this way. They are meant to come off the spool from the end so need to be laying down on a horizontal spool holder. Many of the older machines only have a vertical spool holder. You can always put this kind of thread in a cup that sits on the table behind the machine so the thread comes off the top of the spool if you don't have a horizontal spool holder. Thread doesn't absolutely have to be in the proper position to work but generally they do work a little better that way.