Really the only way is to play them. A LOT. How good you get at the instrument is a combination of how much talent you have, and how much time you spend with the instrument, scales and arpeggios included. The latter is far, far, FAR more important. There are no shortcuts, really. The only shortcut I can give you is keep it fun. If you get bored, play something fun, play along to a recording and just rock out, don't worry about how you sound. Just play. Then go back to doing your scales and working on technique. When you're tired if playing, go do something else and come back to it. Don't force yourself to practice when you don't want to, because if you don't really want to, you're really not going to get much out of it.
Just play when you want to, how you want to, and keep it fun. Gaining skill doesn't happen quickly. It's all about familiarity with the instrument and muscle memory. Even if you feel like you've peaked, keep playing and I 100% guarantee you will get better. A good thing is to find the bassist who your style and sensibilities match up with. For me, it's Geddy Lee, and I find his stuff really easy to learn and pick up, because it makes sense to me.
I'm no teacher, but at the risk of sounding pretentious, I have an extraordinary gift for music (so I'm told

), and I think that even in my humble experience, I have something to offer those less experienced than I.