The G line is the lowest line in the bass clef. Notes may be written below the G line, but they require the use of ledger lines to be read properly. To add ledger lines, you simply draw a line through the note to create a makeshift staff that extends below the full staff.
The B line is the second line on the staff. On either side of the B line there is an A in the space below it and a C on the space above it. A trick to remember this line is the phrase Good Boys Do Fine Always, where G is the lowest line and B is the second line. Moving up from there, you can easily get the rest of the lines of the bass clef staff.
The D line is usually easier to remember because it divides the staff in half. There are exactly two lines above and below the D line. The note on the space directly below the D line is a C. The note that is directly above the D line is a E.
The F line hold special significance in the bass clef. The F line is surrounded by the two dots of the bass clef. It is for this reason that the bass clef is also sometimes referred to as the F clef. If the dots in the bass clef were moved to another line, that line would become the new F line and all of the other notes would transpose to fit.
The highest line in the bass clef is the A line. It is a musical third away from middle C on the piano, which is the place at which the treble and bass clef overlap. Any note written above middle C can be written in either the bass or the treble clef. Although, in most music, the original clef will be used even if that means writing in several ledger lines. The note directly above A is B and directly below it is G.