- Practice mindfully
- 1,2 4 fingering (Simandl upright method) below the 12th harmonic
- Use tools like tuner, drone and metronome
- Tuners and metronomes do not lie
- Set aside a few minutes practice time specifically for intonation
- Record yourself and listen back
Either lined or unlined fretless bass, the Simandl upright fingering was developed for intonation.
Simandl = 1,2 4 fingering below the 12th harmonic. Go to 1,2,3 or 1,2,3,4 when higher up. Thumb on the back of the neck and don't angle fingers.
Get a good tuner. That Korg in the photo is a tuner, metronome, drone and records. Be aware of the 'lazy ear'. Lazy ear develops because of unmindful practice. Can happen over years and you won't notice it. Playing fretless in front of the tv is a waste of time, don't bother. Ok for fretted bass just to flex some fingers.
Like some singers sing kinda in tune, but notes in phrases are out of tune, this can happen on fretless. You hear singers do it all the time on 'The Voice'. Fretless players fall into this. Don't!
Practice bass patterns carefully, stop and check notes with your tuner, open strings and harmonics. You can play with your eyes closed or in the dark. Play a chromatic scale then check it with an open string or harmonic to hear how in tune you really are. A drone can be useful.
Know your board 100%, right to the top. This means every note you can play, know it's name. That goes for fretless unlined, lined, and fretted. Be able to name the notes you play (out loud or in your head) one end of the board to the other.
Don't rely on visual patterns, that's too easy. Minor/major, diminished, half dim etc triads play one end to the other and name the notes. Same for scales in all keys. Every pro, and good amateur can do this. It's not that hard as notes above the half of the 12th harmonic are simply the same as the lower half.
Make your ears do the real work, don't get lazy with the tuner.
Set aside about 20 minutes each practice specifically for intonation. Try to think of intonation practice as putting money in the bank. Then go crazy and play whatever turns you on. Start spending the money.
1,2 4 fingering may be awkward and un natural at first but will pay off with good technique and intonation later. Higher on the board 1,2,3 or 1,2,4 or 1,2,3,4.
This vid of Federico Malaman shows great left hand technique.