Yes, bass is a piece of cake once you understand some basic facts. Your 6 string will flow right into your bass.
1. We play notes not chords.
2. I rely upon generic riffs, i.e. Root-5, R-3-5-3, R-4-5 etc. Get some generic riffs into muscle memory. I have some "how to play bass" instruction books that have 50 or so generic riffs on CD. Play them all and pick your 5 or 6 go to riffs. Get them into muscle memory. What the heck, here are mine:
R-nothing
R-5
R-4-5
R-3-5-3
R-3-5-7
R-R-3-3-5-5-6-5
R-2-3-5-6 this is the major pentatonic which is a gotta have riff.
www.studybass.com has a section on generic riffs that you will want to spend some time with.
3. Decide on how you will sound the notes, with a pick, with your thumb or with your fingers. IMO which ever way YOU like is the way to go.
4. The bass strings will sustain a sound - most call it fret buzz - so you will need to understand how best to mute unused strings. That will depend on how you are sounding the strings. I use thumb and palm mute or a two finger, index, middle motion. Index for the sound and middle for the mute.
www.studybass.com is the place to go for free lessons.
6. Practice playing with backing tracks.
http://www.youtube.com/watch?v=bUK5p...eature=related Accomplishes several things. A.) You get used to hearing the chord changes and getting the "correct" riff going for this specific song. Most of what we do is left up to us, i.e. listen to the song and then decide what baseline we will use is 95% of what we do. B.) You gotta play with other musicians - those backing tracks can be your other musicians. C.) Catching the chord changes and knowing what baseline to use is really what we do. Practice with backing tracks makes it fun.
7. Your 6 string will flow into your 4 string just remember we play notes not chords, but, if you played rhythm acoustic guitar and jammed a chord progression the bass will be a piece of cake.
8.) The 4 string note placement is really easy. Visualize the major scale - it's all over the fretboard, you just have to place the root and then grab your generic riffs notes from within the major scale pattern. I've got several posts where I talk about "Where is your 5, yep it's always up a string and over two frets. Then the 3 is also in it's same spot - up a string and back a fret." Find one of those for the rest of the story on where the scale degrees are.
9.) Should mention we fret right on or just behind the fret - not like we do on acoustic. If you fret like you did on the acoustic you get a bunch of fret buzz -- right on works best. Your old scale patterns will take some tweaking so you land at the correct bass spot.
Have fun.
