The electric Guitar, told me to improvise a bass line, and I did try, but I just ended up embarrassing myself. He told me after that I should learn about the chords on bass or something like that. So, how do you guys make up/improvise a good bass line?
OK from the top. Music is made of melody - what the solo guys/gals sing or play, then harmony - what we as beginner bassists play - then rhythm comes into the picture. I'm going to speak to harmony and rhythm.
Harmony first. If the melody line (treble clef) and the bass line (bass clef) sound good together we get harmony. This happens when both lines share some of the same notes.
Simple way to do that is to
first know what chord is active at this point in the song then play some of the notes of that chord. If you do not know what chord is active hitting some it's notes in your bass line is hit or miss at best.
How do you know which chord is active? Two ways of doing this; sheet music or your ears. As the songwriter has already picked the chord that will harmonize most of the job is already done. All you have to do is play notes of THAT chord. OK which ones? Right at first - the root and fifth note of that chord - to the rhythm the drummer is laying down. IN 4/4 TIME - the root on the first beat than the 5 on the third beat.
As a beginner I bet your ear has not kicked in - so play from sheet music until it does kick in -- a year or so down the road.
Roots first, then the fifth, the eighth is a safe note after the fifth. After that the correct 3 and 7. Minor three gets a b3 and so will the dominant seven b7 or minor 7.
Don't find many 2's and 4's in the chords we normally run up on so.... we've talked about the R, 2, 3, 4, 5 and 7. That leaves the 6 and 8, both of those will flow with any major progression. R-5-8-5 or R-3-5-6.
All you now need is where they are on your neck - in the keys you normally play in.
Good luck.