As bass players, we tend to hold down the fort by playing the root. But when you launch a fill or solo, starting on the root may sound tired. Starting on the 5th is usually a safe bet. The 3rd also works well. In fact, any chord tone other than the root works. If you want to start out dissonant, grab a non scalar tone and then slide back into the scale on the next note. Think of solos and fills in terms of mimicking speech and telling a story. Think of your tone of voice when you start the story. Then find the note pattern that matches that to kick it off.