| Keep your fingering consistant, if you use 'one finger per fret' system, don't change that futher up the neck even though the notes get closer.
Make sure you can get your intervals in tune, Octaves first then fifths and then fourths. IMHO it is easier to hear the 'Perfect' intervals (4th, 5th, octave, unison) than to hear the others.
When practicing ALWAYS make sure your bass is in tune.
When practicing scales or anything,check and check often with open strings.
As you know, the intervals become closer as you move up the neck, so make sure that you learn intervals over the whole neck. One exercise that I like to use is a simple Blues progression (I-IV-V-I) and move it up and down the neck like this: In the Key of C, play the 'I' chord starting on the 3rd 'fret' on the A string... then move to the IV chord but stay on the A string.... when you move to the V chord shift down to the E string (3rd 'fret') when you move to the I chord stay on the E string. This way, you play a sound that is familiar and that you can clearly hear the intonation AND you get the advantage of feeling how the distance between the intervals changes as you move to different places on the neck.
When I learned fretted bass I would go through scales and all kinds of fingering exercises, but I'd move up and down the neck chromatically (fret by fret). As I learned frettless I found that the same exercises were good.... but instead of moving chromatically I've found that I get better use of my practice time by moving around the circle of fifths (C,G,D,A,E,B,F#,Db,Ab,Eb,Bb,F) or the circle of fourth (same thing backwards) either moving across strings, or staying on the same string.
Good luck. Once you get used to frettless, you'll find that there are areas of you musicianship that you haven't known before, there will be new and different musical ideas at your fingertips and your fretted technique will improve.
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Never confuse beauty with things that put your mind at ease. -Charles E. Ives
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