Bass is heavier than a guitar. The body is bigger, the neck is longer. Get your posture right early or your shoulder will pay for it in three months.
Standing position
Strap on, bass hanging at roughly belt level. The neck angles up at 20-30 degrees. Don't let the neck droop, that forces your fretting wrist into a bad angle.
Sitting position
Same as guitar's casual position. The waist of the bass rests on your right thigh (if right-handed). The neck angle is slightly higher than guitar because the bass is longer.
The plucking hand
For fingerstyle (the most common technique), your thumb anchors on the pickup or the lowest string. Index and middle fingers pluck the strings.
The alternating motion: index plucks, then middle plucks, then index, then middle. The two fingers trade off so neither one tires out.
Drill the alternation
Hold any open string. Pluck the string with your index finger, then your middle finger, then your index, then your middle. Even, steady, the same volume each pluck.
60 BPM. Four plucks per beat (sixteenth notes). I-M-I-M-I-M-I-M. Loop for two minutes on the open A string.
Thumb anchor
Your thumb stays planted, either on the pickup or on whichever string is below the one you're playing (the "floating thumb" technique). When you move from the E string to the A string, the thumb moves to the E string. This mutes unused strings so they don't ring.
Next: the major scale on one string. The fundamental pattern that explains why frets are spaced the way they are.