The best way to improve at sightreading is to get a book of music that's not too difficult for you, and spent a little bit of time, daily, playing through it. It isn't necessary to do it for an hour at a time; the key is consistency.
Even 5-10 minutes daily will make you a fluent reader over time. As the sightreading becomes easier for you, you can move into slightly more difficult music. But still play easy music too. It's like with language; the words you're reading right now aren't particularly difficult, but reading and using them daily keeps you fluent.
Each time you start a piece, decide in advance if you’re going to keep a steady tempo or not. And if you are, then don’t stop, no matter how many wrong notes you play. Don’t let it fall apart. Keep something going, even if it’s just the melody or bass line.
But you don’t have to keep a steady tempo all the time. Mix things up. Sometimes, the music’s challenging enough that it’s helpful to slow down here and there to analyze a chord or a rhythm. Don’t stop and repeat it, though; you’re just making sure you play it correctly. Then, play the whole piece again, this time in a steady tempo.
Remember, your goal is to become fluent at whatever level of music you like to play. Even professionals can’t play the Chopin Etudes at first sight. Some pieces are meant to be hard enough to require practice! Rather, your goal is to be able to sit down with a piece of music at your level and basically be able to play it without thinking too much. Just like you can read these words. And since you learned English, you can learn to read music.
Think long-term. You won’t become a fluent sightreader overnight, but you will in a year. And that’s not very long for a life-changing skill like this, is it? Think about it: a few minutes a day for only a year, and for the rest of your life you’ll be able to look at the music you like and either read it at first sight, or get a big head start on perfecting it through practice. That’s pretty amazing!
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