Many of the problems that bassists encounter are caused by a weak and imprecise left hand. As you learn more difficult lines that include string skipping, unusual fingerings, and fast contrary motion, you will need to play special attention to your left hand technique. There are many exercises for the left hand, but one of my favorites is called The Spider.
I first saw this exercise on a John Pattitucci instructional video. It isolates and strengthens each finger. Make sure and start slowly (a metronome is helpful) and speed up gradually. Start the exercise on adjacent strings. Take frequent breaks when you work on these. Tendinitis will sideline you for weeks. Don’t injure yourself!
Here is another more complex version of The Spider from Francesco Consalvo. I would master the one above before working on this one.