I feel like my art looks like a gazillion times better since I’ve adopted this technique.
I saw this advice from a YouTube video(sorry I don’t recall the creator…) who mentioned one common beginner mistake is to have the same line thickness. Of course he was talking about digital art buuuut this can easily be applied to traditional illustration. 
If you look at my before:
My lines are all the same thickness so I think my current work looks better. The nice thing is I can always go over older pieces I deem worthy to update the line work.
