MARTINSR just gave you some really great advice. You really want to not rush it and concentrate your effort on the run only! It seems to me,the condition you've described is actually more of a Sag. So,as a little help,I like to guide-coat any Run or Sag;that's how I was taught and can be a huge help.
A "Run" to me, is like a kid with a very runny Nose.It kinda charges its way down to his lip hopefully stopping just before it enters the mouth. It may have a bit of a Ball on the end,sometimes at the end of that Ball,it'll look like a thin little Rappelling Rope and a tiny Man sliding down safely where it touches the floor of your shop.That,is just a couple of different types of "Runs" where I like to employ the "Razor Blade"technique.