Ok when I write melodies and chord progressions on guitar how should I go about creating a bass line for it? I know that whenever the bass notes change you are changing the upper harmonies of what the other guitars are doing.
Last edited by iidunno at Jan 30, 2012,
You use the scale associated with the key to figure out lines that emphasise chord tones.
And no, Guitar Hero will not help. Even on expert. Really.
Are you talking about a separate bass line or the bass notes you play on your guitar? A bass player will usually attempt more than a guitar player, after all they have nothing else to think about.

In either case generally start with the root note of a chord on the first beat of the bar. Generally the bass line defines the chord changes so you need the root at the point where a new chord is played. The other thing I would look at is the concept of a leading tone where the last part of a bassline before the chord change is a note in the scale of the next chord, often a maj or min7. So if you were moving from E to G then you might play F# as a passing note just before the G. It kind of warns about a chord change and sounds like you know what you are doing.

The other thing about bass lines is that they are rhythmic devices as well having harmonic functions. A lot of bass lines never leave the root but instead vary the rhythm for extra colour.

Beyond that you really need to study bass either by listening to and learning other songs or by studying music theory. 5 years bass and I've only scratched the surface.
Last edited by Phil Starr at Jan 30, 2012,
train your ear, number one. the very fact that you're asking this question is indicative that your ear is not trained.

two - everything everyone else said.
Anfangen ist leicht, Beharren eine Kunst.
give me a bass line you like and we can figure put what they're doing. may give you an idea of what you wanna do.
The only way you're going to answer this question is by spending some time listening to and analyzing basslines.

Bassists tend to know a ton of theory, so understanding that stuff may be hard. But ultimately, there's not a quick-fix answer here. Analyze the bass parts to 20 songs you like and see what you figure out - and you'll know more than most of us giving answers to this question about how to come up with a bass part.