I use:

(sequence "BACKLOG(b!)" "TODO(t!)" "DOING(o!)"  "|" "DONE(d!)")

I treat my Task sequence as a form of a non-visual Kanban. I self-impose workflow limits on the number of items that are allow to be DOING (currently in process) and TODO (committed to doing). I use BACKLOG for items that I have captured but not necessarily committed to yet. I try to always select work from my DOING list. If that has space available in the workflow limit I review my TODO list and “pull” into DOING. If the TODO list has space available, I review BACKLOG and pull forward into doing. I have agenda view for each of these “Kanban Lanes”.

I have a grand thought of someday writing an agenda view or mode that looks like a Kanban board -- I've seen some of what can be done with respect to views in Emacs from the ~calfw~ package, so it is just a matter of time.

Other's have mentioned ideas like waiting on someone else, needs to be verified, etc. I keep those as a separate ~org-todo-keywords~ sequences so that I can use ~S-<left>~ nearly exclusively as my keystroke to “pull” an item forward in the value stream. So for completeness, my task sequence also includes:

(sequence "WAITING(W@)" "VERIFY(v@/!)" "|" "NOT_DONE(N@/!)")

(sequence "ERRANDS(E!)" "|" "DONE(d!)")

I only have to use a direct task selection (not S-<left>) when moving a task out of the main flow into WAITING or VERIFY or moving a task back from WAITING or VERIFY into the main sequence. 

HTH

Mike