A lot of guys ask me to give them some bass-lines that they can use for praise and worship. I simply tell them to know their progressions very well first before they start thinking about bass-lines. Chord progression is the rudiment of bass lines and, if you know your chord progressions very well, bass lines would be something you can improvise as you play to any given song.
Lets take a look at this song sang by Lara George for example; "hallelujah".
The chord progression of the song is
F C G C
fah doh soh doh
To get the bass line out of this progression, there is something we call "chord tone"
A chord tone is a note that can be played along-side a chord that would give a meaningful sound.
The chord tones for the 1 chord(C or doh chord) can be:
C,E,G i.e d,m or s
They are the chord tones because they are one of the elements of the 1 chord(C or doh chord).
Another example: What are the possible chord tones for the 4 chord(F or fah chord):
Tip: just bring out all the elements of the F chord:
They are F A C
f l d
Now lets get back to business
How do we get the bass lines from the progression since we now know their chord tones
The chord tone for G is G B D
s t r
lets start with F
We can choose to rearrange the formation of the chord tones in an order that suits us and that suits the timing of the song; we are free to even repeat some particular notes too
Now for the fah chord the bassist used f f l d f
for the doh chord he used d d m s d
for the soh chord he used s s t r s
for the doh chord he used d d m s d again
but if you are not comfortable with that shape on the guitar as a beginner, you can start with the very basic method by using the chord tones directly as they appear in the chord, see an illustration below:
f l d f l d
d m s d ms
s t r s t r
d m s d m s
Now that's how you improvise, just make sure you are following the timing. The video is coming soon.