well, i picked up bass before guitar
reason being, the bass is the part of the song you feel, and a good bassist can make an otherwise terrible song good by giving it a melody/groove
that's the most important thing to remember as a bassist, you ARE the melody, even if the guitars are playing dumb ass stop riffs for an entire song, you still have the ability to groove it out & make those heads nod
another thing is not playing root notes the entire time, but knowing when to play them. I hate those bassists that just follow the guitars for an entire song, that just shows a lack of talent & makes it look like you play bass because you think it's easier than guitar. But if you pull double time the entire song & rarely throw in a root note, that just makes it look like you're a total showoff idiot. Which you are.
so, yeah, that's what i look for in a bassist
unless it's an upright player