Some good ideas here already and I've done some of them myself. Some things that worked *for me* personally:
- Practice. I know that's very basic and probably sounds condescending and/or smart@$$, but it's the truth.
- Transcribe original pieces I have to develop as part of my lessons rather than just working them out and coming in and playing them. Writing seems to help my reading a lot.
- Don't use books that have tabulature, even if they also have standard notation. Some people might have no trouble at all ignoring the tab, but it's unfortunately too easy for me to cheat. So I try books that don't have it all. (Does that mean I never use tab? Nope, I do. But since I'm paying money for lessons I choose to spend that money on things that will make me a better and more well rounded musician. If I choose to use tab I'll do it on my own time, when it's "free"!
- For me, the biggest issue when sight reading is starting in the right position and also beginning transitions to a new position early enough to get me where I need to be on the neck to play later passages. So, before even starting to play it, I first scan the piece and make notes of where I want to be at given points and also when I should start the transition to that position.
- Related to the previous post, I look for what the lowest notes and the highest notes in the piece are. Sometimes that tells me I'll hardly have to shift position at all and might be able to pick one that makes the whole piece playable there.
- After learning a piece, try playing different parts in different positions. Sometimes after playing a piece well I find a different positions that makes it significantly easier to play.
- Learn to read/play a piece on both a five and on my four. The four often requires more position shifts and I find that forces me to read ahead farther so I can better prepare for the shifts.
- Break up a piece into parts that can be played in a given position and work on them separately for a little while. One benefit is I can get some immediate success by playing parts of it. Then once I'm playing individual sections with some proficiency, then I work on the transitions between them so I can put the whole piece together. Sometimes that forces me to re-work how I play a section, but that's just part of the process.
Can I sit down and simply sight read a piece. Nope. And I'm not sure I'll ever get to that point. But learning to read is a good skill by itself, plus I'm also finding other benefits from sight reading that I hadn't anticipated, so I keep at it. Never stop learning!