By having previously familiarized yourself with the fretboard, you should be able to ‘absorb’ scales into your guitar vocabulary, with little effort.
Just so you know, the scales that you learn in a regular six string guitar are exactly the same as those you would learn when doing bass guitar scales. The knowledge you gain when using the six string axe will come in handy even when playing a bass guitar.
1. There are two basic ‘must know’ guitar scales, and these are the minor guitar scales and the Major guitar scales. This is the foundation of everything else.
Even for pentatonic guitar scales, which by definition are five note scales (hence the ‘penta’ like in a pentagram or pentagon), you would be making use of a minor or Major element.
In fact, the minor scale is actually a Major scale, but starting off two steps backward. This is also known as the ‘aeolian’ mode. So ultimately, if you know just this one Major scale, you would also have the foundation by which to learn all else.
2. People are going to tell you that you have to learn “jazz guitar scales” or “metal guitar scales” but these are actually misleading, as both will still be derived from your knowledge of the basic scales.
A scale for heavy metal, for example, most likely uses a minor mode or a minor pentatonic.
And scales for jazz are so varied that an umbrella term ‘jazz’ is so inadequate in specifying what it is you want to do.
You could be doing a diminished pattern, or merely playing a minor arpeggiated iii chord, which are entirely different things.
Nonetheless, jazz will help you with improvisation guitar because you have to continually adjust your notes according to the underlying chords.
3. You may have read earlier that getting familiar with guitar theory is more important than guitar technique. Well, now you have to know how to build up chops like never before.
As a bass player, who uses wide fretboards, it is advised that you already practice on your bass, as opposed to a regular six string. You need to familiarize yourself with the feel of your instrument.
Even though a bass guitar usually does not have to play single notes in succession as though doing solos, you are inevitably going to have enough skills to showcase your talent.
4. To improve technique, the one tool you need is a metronome. No other device could accurately gauge and progressively raise your technical abilities as a device that ticks at a given tempo. Over time, you must be able to play along even at faster tempos.
Say you start at a tempo of only 80 beats per minute. You can begin with any one of many bass guitar scales from the first position, after which you slide to the second position, until you reach the very end of the fretboard, and you go down again in a similar fashion.
From 80 in one week, wherein you have allotted a certain time each day or every other day for practice, go up to 84 in the next week. Before you know it, in just a little more than half a year, you will be going at it at 200 beats per minute! Good luck.