Hi guys.. I'm here bitching again

The thing is I would love writing basslines like duff McKagan and other people in that genre.. However, I JUST CAN'T GET THAT HEAVY LINE.

Any suggestions how to get that thing going??
How do you start making your lines??
Cort Action 4 string
Hughes kettner bassforce L 100w amp
Line 6 spider 2 amp
Ibanez GIO
Landola Nylon Acoustic
It all falls back to scales, and possibly the melody you want to create. If you practice your scales attentively for like 30 mins to and hour everyday, your lines will greatly improve once you realize how to incorporate your scale work into a given song piece. As much for melody, this is for me personally, I look at it as the bass wants to compliment the guitars sound weather the guitar is playing a power chord or some lead lick, but you never want your bassist to overdo something. Know your limitations and your scales!