One of the most effective tools a pianist can learn is the ability to sight-read. This is the skill that every piano student aspires to. The ability to simply look at a piece of music and just know the proper keys to play. The truth is that this is a skill that should be developed throughout every level of playing. It is also a skill that most piano students tend to avoid. In my opinion, students would never avoid this if they knew how quickly this skill can improve. Now, I am not saying you will be able to play Rachmoninoff within the week. What I am saying is that within a week, you will be better. And a week after that, you will be better. And you will very quickly find your sight-reading has improved greatly. So, let's make sure to practice it properly.
First, make sure you are playing at the right level. Talk to your teacher about what music you should be using for this exercise. There are also some great apps and online resources for this. Again, make sure you're using the proper level. Anything too easy won't really be improving your skill. Anything too difficult will become too frustrating.
1. Study the music first. Put the music on the piano and simply study it. Make note of the time signature, key signature, notes, etc. Take as much time as you want in the beginning. Later, you can work on quickly moving from piece to piece, but for now, no pressure!
2. Play. Once you have made note of the time signature, key signature, etc., just play. Yes, it may be excruciatingly slow at first. But just play! This is sometimes the hardest part. We want to believe that sight reading is a skill that is difficult or even impossible to master. Really, it's all about the amount of time you have spent mastering it. It is literally reading. Just like learning to read a book, you did not master it in a day, but you did master it! As I mentioned before, this is not something you will suddenly be able to learn in a week, but you will see improvement much quicker than you probably anticipate. But this should be a DAILY practice. If this is something you only do during your lesson time, or just once a week, you will not see the improvement you want. If you only have five minutes to practice, practice your sight reading!
3. Don't stop. Now, this is the part that's going to feel so contrary to everything else you practice on the piano, but when sight reading, don't go back to correct yourself. Pick a tempo. Stick to that tempo, and just play straight through. This is so KEY to sight reading. There are several skills that are being developed when a person practices sight reading. (Honestly, this is a fascinating topic, and maybe I'll write a whole post on it later.) But one of the most important skills you're practicing is the ability to quickly read the notes and translate it to the keys. When you stop to correct what you have played, you are not developing this skill. When you stop to correct yourself, really, you're no longer sight reading. You are now practicing.
4. Play it through one more time. Now, truthfully, you can play it through again and again as many times as you want, but as I mentioned before, at some point, you're just practicing another song. Which is fine. If that's what you're going for. In my opinion, you can play something about two times before it becomes practicing. Even the second time, you are probably playing some from memory and some from reading, but I always like to play it through at least twice just so I can correct some of the things I may have missed.
Ok, all this to say, sight reading is doable. It is an incredibly important skill, and honestly, it will make your life easier in the long run.