Placing your thumb on the side of the fingerboard is good! Generally place it toward the bottom of the fingerboard and on the side, not underneath. Pluck over the fingerboard, toward the end of it. Any lower (between the bridge and fingerboard)gets awkward and if ever using a bow will get rosin on you. Use the SIDE of your first finger. This pulls the maximum amount of tone from the instrument. Use the weight of your arm to fall and pull the string. Keeping the finger / hand / arm RELAXED (of course). It should be one motion with the arm and everything. Don’t use just the base joint of the finger, although it should be relaxed and may bend, just don’t initiate the pluck from that joint. This will use the greatest amount of weight possible for volume and after practice speed will not be an issue. Most students think that 2 fingers is optimal, and for some extremely fast pieces this is used, but 1 finger used this way will get a great sound.
Think of the arm as falling (gravity pulling it) down and bringing the finger with it which pulls the string.
This concept is much easier than it sounds!
When I pluck on the E string the string makes a weird metal sound. How can I fix that?
Yumi, that weird sound is the vibration of the string (called “excursion”) being so large that the middle of the string (called the “belly”) vibrates against the finger board. Focus on the direction that you pluck the E-string. Take care to pull parallel to the curve of the fingerboard under the E-string. The opposite would be to pull the E-string up and away from the finger board. On student basses where setup (bridge height, fingerboard scoop and fingerboard curvature) is not optimal, you may have difficulty plucking the E-string w/o it hitting the finger board. Have your teacher take a look at your bass — you might be able to nudge the bridge towards the E side f-hole, and/or raise the bridge a bit if you have adjusters. Good luck!