Note Intonation
On a regular basis, each fret marks a certain note. The bassist only needs to delete the note behind the right edge to produce the correct note. On a cheeky bass, the bassist must hold the string against the fretboard at exactly the right point to produce the desired note. Even small shifts up and down the slope make the note go flat or sharp. Exercising intonation is an important aspect of playing uneven bass.
Develop proper intonation
When playing a fretless bass, it is a good idea to make sure the bass is set correctly, even if the open strings are not Used. This ensures that the location of each note is always in the same place each time the base is played. This allows the bassist to rely on muscle memory and not have to play clean ear.
A training exercise is to play scales up and down each string, and then play the scale across all strings. This helps to develop the ear, the connection between the ear and the hand when intonating the notes and the muscle memory used in the scale. It is a good idea to check notes sometimes against a keyboard or other reference height. Even if the intervals are perfect, the notes may still be a little out of sync with the actual root note.
Vibrato
Using a fretless bass opens up a new method of producing vibrato that is not available on a fretted bass. Start with a first note, slide your neck down just enough to hear a tone change. Then you return to the first note. Switch between the two places quickly to form vibrato. This is the same method as a violin vibrato is played. The advantage is that the actual note is the higher note, as opposed to the lower note with the traditional bass vibrato. The ear naturally sucks at a higher pitch, which makes this way of vibrating sound a little better for the listener. Playing a fretless bass allows the bassist to make minor tonal changes that are not possible on a corroded bass. Musical techniques such as vibrato and legato are easier to use. This allows for an often softer feel for a baseline. It is also more difficult to play because the bassist needs to properly intonate each note without the help of the frets.
Source:danspela.com