As Fergie said, the two main pieces of information you need when reading are the rhythm and the pitch. Other score notation can be slotted in once you've got the rest down.
If you are struggling with the rhythms, put the bass down, set your metronome going and just concentrate on clapping the rhythm. Break beats down into subdivisions and slow the tempo if you find a really tricky bit. When your reading is up to scratch you should be able to clap out pretty much anything at tempo.
If you are struggling with the pitch, pick the bass up, set the metronome going and ignore the rhythm. Just read the notes and play a note on each beat. That will help you to link the notes on the fingerboard with the notes on the page.
Once the rhythms and pitches are cemented in your mind, sight reading becomes much easier. Also, as other have said, just play stuff as much as possible. Start with simple things and gradually move to more complex things as you become more confident, but try and practise at tempo as much as possible - only slow small sections down if you are struggling.
If you are struggling with the rhythms, put the bass down, set your metronome going and just concentrate on clapping the rhythm. Break beats down into subdivisions and slow the tempo if you find a really tricky bit. When your reading is up to scratch you should be able to clap out pretty much anything at tempo.
If you are struggling with the pitch, pick the bass up, set the metronome going and ignore the rhythm. Just read the notes and play a note on each beat. That will help you to link the notes on the fingerboard with the notes on the page.
Once the rhythms and pitches are cemented in your mind, sight reading becomes much easier. Also, as other have said, just play stuff as much as possible. Start with simple things and gradually move to more complex things as you become more confident, but try and practise at tempo as much as possible - only slow small sections down if you are struggling.