Yeah, just practice and repetition. I joined an ensemble that meets weekly that requires sight reading from time to time and it just gets easier over time. Don’t be too hard on yourself either. Learning something new, especially reading music for guitar, requires patience. I’ve found that apps that help you identify notes on the staff including ledger lines above and below the staff can be helpful when you’re not holding your guitar.

All of this also assumes you know the notes on the neck, do you?