First, you have to practice a whole lot! It doesn't hurt to memorize the song, but if you're like me and aren't good at remembering things (especially something like the Mozart Turkish March! If you can play that, Kudo points for you!) you might try something I do. If I'm trying to read notes while playing the piano, I say the names of the notes as quickly as I can, and after a while, I just know where to go, so I'm able to play quickly. If that doesn't work.....I guess practice is the other good option. Whatever you choose, I wish you good luck!
If you mean sight reading it's a skill and to learn to sight read very well sight singing will teach you. It's a class in all community colleges and it's helped me beyond the scope of my imagination. One thing that always helps is that while I'm sight reading I know what it's suppose to sound like and so when I play if I hit a wrong note, I know it. You also must practice sight reading for your individual instrument (piano in the case that you mentioned) and you learn to read ahead of where you actually are playing. The Turkish March is entirely sight readable but it's not easily sight read. Yes in most cases the Musician memorizes the notes (in piano your not suppose to have the score in front of you at a recital; you suppose to memorize the piece) (Franz Liszt once made a bet with an amateur composer and the composer said he could write a piece Listz couldn't sight read. Listz took him on and it was this horrible piece that was stupidly fast and in the end it ended with Franz Listzs hands playing two chords far away from Each Other and a note in the middle. Franz Listz had a huge nose and he bent down and played the note in the middle with his nose; this story quite possibly didn't happen but it's funny anyways).
Edit: To read both lines you read the bottom first always but eventually you learn to read them together. It's very similar to speed reading for reading words. You learn to read multiple lines together and the double spaced font becomes impossible to read.
When you practice everyday you get better. You can read faster and your figures move faster because you are familiar with the keys. It's like typing on a computer keyboard.
I like to start off slow, making sure I hit every note, then play it with the rhythms, and then just get faster and faster every time!
well...........you have to practice, remember.....practice does not make perfect, .....practice perfect makes perfect, and ya most musicians do!
its mostly practice and memorization. been playing piano and still play so slowly because of that! no idea how they do it .. ha ha
Practice a lot. It will help you memorize them when you're playing the music.