Set a consistent schedule for practice of your sight reading exercises. Even if you can only manage 20 minutes a day at roughly the same time of day for each session, you'll be farther ahead than if your practice is sporadic.
Practice playing your warm-up scales in the dark or with your eyes closed. What this teaches you is to "feel" the amount of physical space between the white and black keys so that you won't have to look down at your fingers while you're playing.
Discipline yourself to keep playing at the established tempo of a piece even if you make a mistake. If every time you hit a wrong note and get flustered by it, this will only get embedded in your subconscious and make it impossible to play a piece completely through. Whatever piece you decide to play, commit to playing it all the way through each time, then stop and go on to something new.
Practice the right hand and left hand movements separately and use a metronome to ensure that you're maintaining the proper tempo. For difficult sight reading pieces, set the metronome at a slower pace and, if necessary, count the beats out loud.
Study a piece of music thoroughly before you play it and lightly circle the recurring chords and progressions with a pencil. The more you familiarize yourself with these patterns, the easier it will be to play each time you encounter them. To return to the foreign language analogy, this is similar to the ability to recognize common words and phrases and--when combined with new vocabulary--be able to figure out what is being communicated.
Jot down in pencil the letter of those notes that extend far above and below the treble and base clefs. This will help you find them more easily and, in time, will become second nature.