Soloing

Scales To Use
major


g----------------------------------------
d----------------------2---4---5---------
a-----------2---3---5--------------------
e---3---5--------------------------------

minor

g----------------------------------------
d----------------------3---5-------------
a------------3---5--6--------------------
e---3--5--6------------------------------

dorian

g----------------------------------------
d-----------------2--3--5----------------
a-----------3--5-------------------------
e--3--5--6-------------------------------

minor pentatonic

g----------------------------------------
d----------------------3----5------------
a-------------3-----5--------------------
e----3----6------------------------------

major pentatonic

g----------------------------------------
d------------------------2----5----------
a--------------2------5------------------
e-----3----5-----------------------------

blues

g----------------------------------------
d-----------------------------3-----5----
a----------------3---4---5---------------
e----3-----6-----------------------------
Application Of These Scales
Patterns: you can use little visual patterns to create interesting lines in solos. Eg: as in each note of a scale a number, 1 through 8. then play 1, 3, 2, 4, 3, 5, 4, 6, 5, 7, 6, 8. That's what I'm on about! Playing these sequences can also help with technique when practiced with a metronome. Here are a few more:
1, 4, 2, 5, 3, 6, 4, 7, 5, 8.
1, 2, 1, 2, 3, 2, 3, 4, 3, 4 etc
1, 8, 2, 7, 3, 6, 4, 5, 4, 4, 3, 6, 2, 7etc

Ideas: you can use little motifs/ideas within a musical context that you repeat on to create interest for the listener. Because of the nature of the bass guitar, bass guitarists are genereally very bad at this and tend to just go through everything as fast as they can. That is one of the reasons teachers will tell you to transcribe horn solos, or keys. Horn players are very good at developing ideas/motifs within a musical context, because they are not thinking scale shapes, they are thinking musically. As in speech, lines should be played in little phrases, to keep the listeners interest. People don't just blurt out a whole paragraph do they? So thinking in short melodies, rather then shredding can aid in making a solo better. of course this takes years of practice. Another cool idea creator is to play the melody and slightly change it each phrase. This does take some practice but when mastered can make your bass lines seem almost horn like in nature.
Other Ideas: playing behind the beat - this is best practiced with a metronome. Playing behind the beat is basically just playing just before each beat, but being consistent, because if your not consistent, you will sound terrible. Percussive solos - just play beats on your strings, this is totally different, and when combined with dead notes and roots can be extremely effective. Chromatics - using the frets inbetween the scale notes can give a jazzy feel, and also add that 'out' sound you will hear horn and keys players create.
Techniques
Artificial Harmonics: I noticed a comment asking for pinch harmonics and I assumed you meant artificial harmonics. Artificial harmonics were made famous in bass by the great Jaco Pastorius. He used these in a more melodic context which has since been utilised by players such as bootsy collins, victor wooten, richard bona etc. An artificial harmonic is played by placing the knuckle of the right thumb on the node point of a string. Then plucking with your index finger. The node point is found twelve. Frets above the note your fretting. If you move up a fret with your left hand, then you have to compesate with your right. The node is usually written above the fretted note in brackets like so:

(15) (17) (14) (15) (17) (14)(16) (17)
g-------------------------------------------
d--------------------------------2---4----5-
a-----------------2----3----5---------------
e-------3----5------------------------------

To practice this technique, it is a good idea to play through scales, particularly widely spread scales I.e 3 notes per string (which you can find in other lessons).
Slap And Pop: slapping is one of the techniques which makes bass unique. To slap a note, hit the string with the side of the knuckle of your right thumb. Pops are the 'rebound' of a slap.(sort of) to pop, simply lift the string up with your left index or middle finger, then let it snap back down onto the frets. these two techniques produce a very distinctive sound, so you I'll know if you are doing them correctly. they are written as below:

s s s s s p p p p p p
g----------------------- g--5--4--2-----------------
d----------------------- d------------5---4---2-----
a--------2---4---5------ a--------------------------
e--3--5----------------- e--------------------------

Once again, play through scales, using these techiques to master them.
Dead Notes: dead notes are used by bassists to create a rhythmic feel within a solo. for the ultimate in dead note usage, look no further then wictor wooten 'me and my bass guitar'. To produce a dead note slap, pop or just pluck a string, whilst resting the left hand lightly on the strings, so the don't ring out. Dead notes are written as below:

g------------------------------------------------
d-------x--2-----x--3----------x--2---x---3------
a------------------------------------------------
e---3-x------x--------x--3--x-------x------------

I don't know what these are called but Victor Wooten uses them alot, they are done by playing an open string, hammering on with one finger, then slapping or popping the next note, ie:

s s
g------------------------------------------------
d------------------------------------------------
a------------0--h--2--3-h-5----------------------
e--0-h-3--5--------------------------------------

Once again, practising these with scales and metronome.
Arpeggios: arpeggios are created by taking the colour tones out of chords and playing them melodically. Example:
a major chord = 1-3-5
minor chord = 1-b3-5
b= flat diminshed chord = 1-b3-b5
#= sharp augmented chord = 1-3-#5
dominant 7th chord = 1-3-5-b7
minor 7th chord = 1-b3-5-b7
major 7th chord = 1-3-5-7
etc

So to put this in context, again, assign each scale note a number,



1 2 3 4 5 6 7 8/1
g-------------------------------------------------
d------------------------2---4---5----------------
a----------2----3---5-----------------------------
e---3--5------------------------------------------

then start combining colour tones eg:
minor = 1, b3, 5
1=G b3=Bb 5=d

g-----------------------3-----7-------------------
d-------------------5-----------------------------
a--------2-----5----------------------------------
e----3--------------------------------------------

These arpeggios can be used to outline the chord changes.
Walking Bass Lines: a walking bass line is created by playing the root (1) of a chord, then 'walking' through other notes to get to the next chord. A good general rule to follow for walking bass lines when beginning is to play (in key of C major) root-c 5th-g root-c leading note (7th or 2nd of next chord) - so if the next chord is F then we could play either the 7th of F-e or the second of F-g.
Bends: bending a string up can add a bluesy effect, and isn't really done by enough bassists these days. A good note to bend is the 3rd note of the blues scale in the second octave, ie:


g-----------------------------------3-----5--------
d-------------------------3-----5---------^--------
a---------------3-----5----------------------------
e------3----6--------------------------------------
Open String Harmonics: there are a few harmonics to be found that can be created with out fretting a note. Jaco was the pioneer of harmonics on bass, so check his stuff out to see the real deal.


g-----------------------------------
d-----------------------------------
a-----------------------------------
e--2.3--3.2--4--5--7--9--12---------