Too many bass players leave their plucking hand technique to 'chance'. At slower tempos a musician can often get away with it, but once one hits a certain speed the plucking hand needs a 'method' in place for the bass player to be able to execute accurately and consistently what they are playing.
 
If you watch an orchestra, you will notice the violin section will all be using the same bowing pattern. This is because they have a method - and they stick to it every single time they play a piece. We want to build this level of self-awareness into our own playing.
 
The best way to build a method is to know what it feels like to play a 'perfect' and 'correct' exercise. This way the hand gets used to knowing what it feels like to play 'right' and can then adapt this to the necessary music.
 
This document is written for 2 plucking hand fingers and for 4 string bass as a series of open-string exercises designed to cover all permutations of plucking hand movement. It is only possible to play an odd or an even number of notes on each string, and these exercises cover all of those possibilities. These exercises are also good to work on string muting, to ensure that only the string played is the one heard, and there are no others still ringing through.
 
These exercises cover alternate picking and raking and are the fundamental exercises I used to develop my (and my students') 2 finger plucking technique. It is good to learn to lead with either finger and to switch between alternate picking and raking by choice, rather than by chance, as I often find I have to calculate the plucking pattern for a tricky line and may play half-alternate and half-raked for my fingering to repeat by starting on the same finger.
 
I would recommend playing these without a metronome at first until the fingering becomes comfortable. A good 'goal' tempo to eventually work up to would be 16ths (semiquavers) at 120bpm, which is 8ths (quavers) at 240bpm. For the triplet phrases this would be triplet quavers at 180bpm.
 
Also available for 5 and 6-string bass.