any tips on improvising fills for songs?
i just have no idea on where to begin O.o

like in the part of the songs where the guitar and drums stop for a few seconds, and the bass does a lick, any tips on making those parts? formulas? ideas? thanks

scales, arpeggios, study them, learn how to apply them in a song. Transcribe your favorite fills, listen to how they flow and accent the song.

I struggled with figuring out fills for a while, there's no real "formula".