I teach sight reading like you would learn normal reading in school. Students do not learn to read by starting to read that they do not understand or cannot read fluently. They would be simply sounding out the words and not speaking in sentences.
Instead of something like: "Today is a wonderful day" it resembles "T..oo..d..ay i ... i..s .... is , a .... a , wen.... wi...wo....won.... wond....er...... ful, d..day."
This might be useful to some people however to most who are developing to read music this is a very annoying way to improve. You have to learn how to read simultaneous things in music with a progressive stepwise study. Like you learn to sound out combination of letters, you learn to sight read chucks of music at a time, you learn to read intervals more effectively, you start to see shape/pattern in the score and how that effects your hands.
However when studying to improve your sight reading you must of course stretch yourself to read more difficult music, then when you decrease the difficulty it seems somewhat easier. It is like swinging 3 mental baseball bats to warm up, then swinging with one, it will trick the mind to work more effective for most people.
We must know to treat reading difficult music to improve our sight reading. When sight reading difficult music we must always ensure we use the correct fingers and correct notes. With easier music we can do the opposite strangely enough to encourage speed of reading. With more difficult music we are aiming to improve our accuracy of reading so we must approach sight reading hard music with a much slower tempo and a lot of controlled pausing (freezing the hands then moving only when you completely consciously understand what to do). Making fingering mistakes and note errors with difficult music does little to improve your sight reading as what you do becomes more and more obscure and more difficult to recover the more errors you make. However with easier music you may do these mistakes and recover very easily.
The problem with constantly reading difficult music is that it does not allow us to learn to read ahead of ourselves. We are so caught up over trying to pronounce the music that we lose several things 1) the musical meaning of what we play 2) the fluidity of what we play, speed/accuracy of reading 3) being able to read ahead and anticipate what is to come next via reading or sound.
Read easier pieces so that you train your eyes to read ahead of what you are playing as we do when we read words this will help you to read more dense difficult works faster. You must learn not to play what your eyes read when they read it you must read before you play, this comes most effectively from playing music at your level (this is a very deceptively difficult level to establish for the individual and one could write many pages on how you are to establish/monitor this, you cannot study pieces that are too easy and you cannot study pieces that are too hard, there has to be a point which challenges but is predominantly controlled.)
Topic: more than 1 year experience with sight reading