Once you understand the syntax of written music, I would also suggest picking up a book like "Vade Mecum" from Slava (George Vance's stuff). It is a really good book for scales, rhythm and other techniques. But for you, the idea is play them and help your eyes learn to track the written page as you play. You also want to begin to form the association of certain positions and shifts common to particular key signatures. The scale and arpeggio drills help with this. (If you play Simandl, you should mark out or at least ignore the position and fingerings written in "Vade Mecum").
I would also encourage you to get the sheets to any pieces you may already know by ear and play those while tracking the sheets with your eyes. Beginner method books are often full of familiar passages. Pick up a few of those if you can. Just play "Twinkle, Twinkle" when no one else is home

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Eventually (I'm just about there!) you will be able to look at the pages and "play" the piece in your head. Practicing this with melodies you already know begins the process. (It also helps you learn to look at the your left hand much less!)
If you are truly talking about sight reading, you want to get to the place where you can pick a piece that is within your technical ability and play it reasonably proficiently on the first pass. So, your goal is to train yourself to associate the written notes with real tones and stop positions on the fingerboard. So if you are working with known melodies and your ears already have the "expectation of pitch, ( foot note attribution here to TBDBer wiser than I) " the associations begin to form more quickly.
If you find yourself in a for-hire, one-time event orchestra, this comes in pretty handy. If you have played it in your head a few times, you have a much better shot at sounding good when the noise starts.