Identify the first left hand (bass clef) note in the piece of music and name what the note would be on the right hand (treble clef), based on its position on the stave.
Count two tones (three notes) up from the note you named, counting the first note as the starting note, e.g. if the note is A, then count "A, B, C."
Play the C note with your left hand. You have played your first bass clef note. This is the two tone rule: between the treble clef and bass clef are two tones.
Go to your next bass clef note.
Count two tones, remembering to count the starting note as one, e.g. a D#.
Count two tones, "D, E, F," adding the sharp sign at the end to arrive at F#. You've worked out your second bass clef note, this time a sharp.
Practise this two tone (three-note) rule to systematically work out all your bass clef notes.
Pencil in the notes you work out as you go until you can fluently read the bass clef without working it out from the treble clef.