I do! I use Asana for staying organized and I have a workflow video of that here: http://www.bombchelle.com/2014/how-i-use-asana/ They’ve updated their UI a bit since I did that video, but the core feature set and the way I use it is mostly the same.
You might also look at Streak: http://www.bombchelle.com/2015/workflow-wednesdays-streak-for-freelance-writers/
If Asana seems like too much for you, you could potentially set up a funnel for each client and then move things along it as you pitch them/work on them. I think Asana would probably be better (and it’ll scale a lot easier as you grow your business), but either of them should work. (I would recommend Streak either way as I found it super useful for keeping track of all of my pitches when I was scaling up my freelance biz to leave my side job!)
Hope that helps some, LMK if you have any more questions — love to chat about this stuff :)