I started off as a guitarist 38 years ago and added bass to my repertoire about 33 years ago as a means to score more gigs. One important concept that I'd like to share is that if a guitarist decides to pick up the bass, they must realize realize a bass is not a 4-fat stringed (or 5, 6) guitar. It's a bass guitar and the technique, sensibilities and approach are different.
It's primarily a rhythm instrument with the ability to add melodic and harmonic elements within the rhythmic context. Once this domain has been apprehended and mastered to a reasonable degree, then sure, one can experiment with other stylistic and flashy elements.
While this â€œphilosophyâ€ is a good and practical way of learning to play the bass for any novice, it's paramount for the guitarist learning to be bassist to understand this and practice it. Otherwise the result is a crappy bassist. These former guitarist bass players are easy to spot as they are all over the neck and have no concept of the groove.
I realize that this should be common knowledge as much as it's been repeated, but in the years that I've taught bass, I can count on one hand the bass students that already play guitar who understand that there is a significant difference in how one plays guitar and bass. Most of the students I've had who have no guitar experience are able to progress in the basics more rapidly than the guitar playing ones. Why? Because I don't have to spend the time breaking bad habits that guitar playing, bass student novices seem to universally suffer from.