I'd like to comment or discuss some of the posts I quote below, but I don't think I'll be able to be involved in a long discussion because my very limited english LOL
Use disciplined 'shapes' or 'boxes'; for example on one entire gig use just one shape (like middle finger on the root of the key etc)
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On the contrary, I always taught & learn to be able to play as many possible 'shapes' for any single key/scale/etc. It helps me a lot.
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For me my improv skills changed almost overnight when I focused on using scales that have the same key signature. IE C-min is the same as E-flat. ...
C minor is different than E flat.
Perhaps if what you mean is C minor Aeolian, then it has same notes in it as the E flat Ionian (Major).
But there are other 'C minor' scales, for example Cm Dorian, Phyrgian, ...and also there are other E flat (Major) scales too, like Eb Lydian, Mixolydian,..which are not the same..
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Learning to play the melody of each new song first before working on the bass line
Something I picked up at Berklee. Don't just play bass lines. When you hear a neat vocal hook, learn to play it on your bass. Trombone line, orchestral part, children's nursery tune... just play them on your bass. Learning to sing them is also a big advantage.
Very very good advice..

not only the song melody, but also other aspect IMHO, like chord/song structure, sound, other instrument in that song/record etc etc,..In short word, don't only learn the bass (line/aspect) of a song.
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EVERYTHING MENTIONED ABOVE, (or below)
.done slowly
Im just a crazed-pain in the butt advocate for practicing slowly, its like, most everyone knows that if there is a problem with a passage or turnaround at full speed, ya gotta try it half speed and if it still sucks slow down even more. In all my struggles with guitar and bass (that still continue), I still have to remind myself, That was freakin sloppy! Slow it down.
Theres no fear that if you practice slow that you wont be able to play fast, you will be able to play fast my friend
. Very fast!
This is also a very good advice...
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Not sure. I've seemed to have had the same basic technique for all my playing life....for better or worse... The pinky thing, I got conscious of that in the early months of playing and focused on that. It sucked at first but you cant play right with just three fingers. Sometimes I actually prefer using my pinky instead of my ringfinger (I mean for stuff that would technically be better to use the ringfinger for)
The only thing I am conscious improved a little in the past say 5 years is my picking speed. Not that it's much use, I CAN pick real fast now but have no use for it in the music I make. I mean like Matt Freeman fast...(though I cant keep it as consistent over a long period of time like he does) I don't care for Rancid but its listening to his solos that motivated me to see if I could pick like that. I should probably like him more, the only time i've ever seen any famous musician with my actual bass (an Ibanez Tr-70, cheap one they used to make) was Matt Freeman in the 90's...
IMHO while Matt Freeman is a very respectable bassist, he's not slow, but also not that 'really fast',..I can't give any example right now, but I've seen some/many other bassists who play really fast.
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Pay attention.
Wait... bear with me. I know "pay attention" sounds glib, but the point is that you should do more than just figure out notes. You should also listen very carefully to the nuances of expression and timbre. Those nuances are what elevate your playing above mediocrity.
Put on headphones/earbuds and listen to a line you're trying to emulate. Record yourself playing the line, maybe just a few bars. Listen to your version and compare to the original. Figure out how to pluck the string, where to pluck it, which string to fret, what tone settings to use, etc. in order to come as close to the sound of the original as possible. Don't worry about what you're "supposed" to do -- just focus on getting the sound. Understanding those details will broaden your palette, and you'll be able to apply those nuances to your playing in general. Try this with a multitude of styles.
And be patient! It takes time.
Word!
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Going back to basics after forty years.
I've developed a few bad habits such as raking strings...
While I agree that basically and generally strict alternate is very necessary to learn from early on until one 'mastered' it, but IMHO 'Raking' doesn't have to mean 'bad'. It has it's use in bass playing, just like other technique, because it can give different 'nuance', sounds etc, (not always about speed, fluidity nor dexterity)...I think it as one of 'technical thing' I'd like to learn and keep in my 'pocket' and use it whenever needed....just like other (picking) technique.
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...always be open-minded towards music; listen and try to play as many various types of music possible. Analyze the tone, rhythm, and style of playing. This goes even more so with what you already enjoy listening to.
Word !
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Oh and I'd like to add one thing:
Chordal knowledge is very important first, but after that, for 'scale type of play' exercise;
Hanon Virtuoso Pianist Exercise,... Practicing that with bass really opens up almost anything technical wise to me... Well IMHO in fact, learn as many other instruments other than bass, whether to play it/them or to adapt it's/their lines into bass is very very good and will make make the player 'different' (in poistive ways) compare to other bass players.