How can u tell...DR/SR

How can u tell if ur DR/SR are about to go up/down? I've seen ppl reference this several times. I'm obviously a newer player. My SR is at S but my DR hasn't changed since I started, which is confusing because from what I understood u improve this by not being in collisions, which I do try to avoid. Of course sometimes there's nothing u can do when ppl are trying to run u off track for trying to overtake then on lap 1, which is so stupid. Are there other factors? I just don't get why I'm stuck at D but my SR is an S. I think I've only won like.....maybe 4 online races. Thanks.