Sight-reading is part of learning to play the Piano. Playing the piano is the other part. How to start? Read-up theory of music! It’s well documented. Get a book on Theory of music. Start to appreciate what are the following markings on the music sheet:
1: What, Where is the Treble, Bass clef on the sheet music what is the composer of this sheet music telling your hands, play with right hand the following notes, play with the left the following notes. How fast should your playing be, what value is each note on the sheet worth with respect to a common time. Play each note, pitch for your rhythm to common time.
2: Analyse all the markings on the music sheet.
3: Learn theory, music theory away from the piano to then sight-read music sheet.
4: Understand music concepts, Time signature, Key Signature, Accidentals, Scales, Degree os scales in an Octave. What are the 7 pitches called? Tonic to Tonic notes. What is a chord? How is a chord denoted on the music sheet. What is Major scale? What is a Minor scale? How are the two modes related and identified? What is inversion of a chord? What is a chord progression? What is a harmony? What is a Melody? All these are noted on the music sheet. It is not written in English but in music symbol to mean how to play, express and play the note and for how long.
5: Take on sight-reading on one hand at a time, the treble clef (Top) for your right hand. Read the notes on the lines of space. A note on each line of space determines the keys to play. For example C, on line as a Middle C.
6: Repeat and practice reading until you read and play at the same time. It won’t come to you first time you try to read sheet music.
7: Repeat Reading more each day
8: it will then become second nature once you understand Theory behind music, music notation and sheet music