Lastly, and this was advised from Josh Wright and I agree with it, feel free to sight read a piece a couple of times. It is still sight reading, and the general idea of sight reading is to improve recognition of notes, which is more easily done if you work with the same combinations multiple times.
I have heard others swear by hymns and chorals to develop sight reading
Always aim to maintain tempo, so be realistic and pick a tempo at which you can sight read the fastest part of the score (despite what people tell you, sight reading is still sight reading even if you have looked at the score already)
For me, sight-reading is literally looking at a score I've never seen ever and trying to play through it.
Reason why I don't recommend hymn books for sight reading is bc the pages they are on and also there usually are song words printed in between the bass and treble clef. This makes it extremely difficult to sight read it as your eyes will be constantly jumping up and down.
Doing everything above is a good idea. Try out the suggestions for a while, and once you see which ones work best for you, do them.Here's some free sight reading stuff I found a while back:https://imslp.org/wiki/Sight_Reading_Exercises,_Op.45_(Sartorio,_Arnoldo)https://www.soundswell.co.uk/pages/swsightr.htmhttps://imslp.org/wiki/Mikrokosmos,_Sz.107_(Bart%C3%B3k,_B%C3%A9la)https://www.belmont.edu/music/admissionaudition/piano_sightreading.htmlAnd as someone recommended above, czerny's progressive studies:https://imslp.org/wiki/100_Progressive_Studies,_Op.139_(Czerny,_Carl)
I have never practiced sight reading except maybe a few hymns for church. Anyways, I'm pretty terrible at it and can't even sight ready easy stuff perfectly. I have never practiced it because learning recital pieces I always just memorized them right off the bat. So obviously I need to practice sight reading... What is the best way to go about doing this?