One thing to remember and I'm still getting used to this too it's that once the run sequence is initiated, your character will keep running, so you let go of forward and block and focus on what the next button inputs are to extend your combo.
So far the timing I use is pretty much the same as the dash was used in mk9 only with that added block button.
Also instead of pressing f,f,bl try f, f+bl so instead of 3 inputs it's only 2.
Again I'm still trying to practice this myself and I'm no expert So I may be doing it totally wrong too....