In this lesson I will show you the techniques I use for playing 
bass solos to hopefully help you write your own. So here goes.

Starting from the start you need some knowledge of scales. The 
most simple types of scale are major and minor and are played 
as follows: major  c to c with no sharps or flats (c, d, e, f, g, 
a, b, c or tone, tone, tone, semi—tone, tone, tone, tone, semi—tone). 
Minor  a to a with no sharps or flats (a, b, c, d, e, f, g, a or tone, 
tone, semi—tone, tone, tone, semi—tone, tone, tone). Here 
are some examples of major and minor scales: 


C Major:
G|————————0—2—3—5—|
D|——0—2—3—————————|
A|3———————————————|
E|————————————————|

E Major:
G|—————————————————|
D|—————————————1—2—|
A|———————0—2—4—————|
E|—0—2—4———————————|

F Major:
G|————————————————|
D|——————————0—2—3—|
A|————0—1—3———————|
E|1—3—————————————|

C Minor:
G|————————0—1—3—5—|
D|——0—1—3—————————|
A|3———————————————|
E|————————————————|

E Minor:
G|————————————————|
D|————————————0—2—|
A|——————0—2—3—————|
E|0—2—3———————————|

F Minor:
G|————————————————|
D|————————————1—3—|
A|——————1—3—4—————|
E|1—3—4———————————|

The usual technique for playing solos is to find out what key 
your song is in and then improvise or write notes from that scale 
over the backing music. When you play over chords you will need 
to know what chords are being played, and then play the notes 
in that chord. So if you are playing over a chord of c major then 
the notes in that chord are the ones, which will sound the best 
(c, e and g). You can still use other notes in the scale, but they 
will not sound as appealing as the chord notes. 

Slap solos.
Nearly all of the bass solo's I've heard have included some slap 
in them. In case you're new to bass, slap is where you make a fist 
and hit the string with your thumb. There are a few ways to incorporate 
scales into a slap solo. One, which is the most obvious, is to 
play a normal solo but slap it. A few others include left hand 
taps (not actually plucking the note but bringing your finger 
down and making a sound) and index finger/thumb pops (pulling 
the string up and letting go creating a twanging sound). These 
techniques will make the solo sound faster, but will require 
more skill to make them sound good. Below is an example of a slap, 
pop, tap solo in e minor: 



G|————————————————————————————|
D|—————————————2—————2—2——————|
A|—————————3P2———3P2——————————|
E|—0—0—2—2———————————————X—3—0|
 S S S S P P T P P S P P

Another way to play a slap solo is to play the notes in a scale but 
slap another note in between them. This "offbeat" note can be 
in the scale or not. An example is shown below 

(this is in a minor)
G|———————————————————————————————————————————————|
D|————————————————————————————2——————————————————|
A|——0———2———3———2———0———2———3—————0———2———3p2p0——|
E|0———0———0———0———0———0———0—————0———0———0———————0|
 S P S P S P S P S P S P S P P S P S P S P S

With the last technique you can change the Es or whatever note 
youre using for a dead note and it will sound just as good. 

Tremolo slap.
This next technique I don't know the name for, when I thought 
it up I didnt know of anyone else who did it so I named it myself 
as tremolo slap. It is a slap technique but it gives the impression 
of a tremolo pick on guitar. What you do is play the normal slap 
note, and then on the way back slap again with your fourth finger. 
If you can get this fast it will sound amazing with a minimal amount 
of effort. I suggest practising scales, but doing them with 
this technique to build up your speed. 

Moving scales around.
The scales I gave as examples don't have to be played like I've 
shown them. These are just the basic majors and minors of notes. 
You can play around with these scales, try flattening the seventh 
of a minor scale for a bluesy sound, or flatten the seventh of 
a major scale for an even brighter sound. The possibilitys 
are only as limited as your imagination! Also, the scales dont 
need to stay within these boundaries, you can move them up and 
down the fretboard as long as you stay within the notes of the 
scale. You can add accidentals to the solo but don't add too many 
as this will make it sound sloppy and in some cases may even put 
it in a different key! 

Well that's all, I hope this inspires you to create better solo's 
and helps you in the process as well. Thanks for giving it a read!