This method involves finding notes of the same pitch on different strings. The diagram that follows outlines the notes used:
One of the easiest ways to practice tuning is to actually start with the bass in tune and then detune one string. When you do this, always take the string down in pitch (i.e., loosen it) as it is easier to tune "up" to a given note rather than "down" to it. As an example, detune the second string (D). If you play a riff or scale now, the bass will sound out of tune, even though only one string has been altered (so remember that if your bass is out of tune it may only be one string at fault.)
Following the correct method, you must tune the second string against the D note at the fifth fret of the third string. Play the note loudly, and listen carefully to the sound produced. This will help you retain the correct pitch in your mind when tuning the next string.
Now that you have listened carefully to the note that you want, the D string must be tuned to it. Pick the D string, and turn its tuning key at the same time, and you will hear the pitch of the string change (it will become higher as the tuning key tightens the string). It is important to follow this procedure so that you hear the sound of the string at all times, as it tightens. You should also constantly refer back to the correct sound that is required (i.e., the D note on the fifth fret of the third string).