Star chart advice/ideas please

[scrappydappydoo]

Having a thick moment...

DD2 (3yrs) is still struggling with poos on the potty and we're also having lots of challenging behaviour from her so I'm going down the star chart route with her however I've sat down and I just can't figure out where to start and what to do and what to actually ask of her and then I got to thinking that I don't actually know how to work it - do I just give stars - should I take them away for bad behaviour?? or what??
AND then dd1 (5yrs) stated that it wasn't fair that dd got to work towards a treat and she didn't (good point) but I don't know tasks to give her - we don't have many problems with behaviour apart from whining - but how can I put that as a measurable thing??
Help - I'm having a truly thick moment - this should be easy but I seem to have painted myself into an over-complicated/over-thought-out corner.. What's on your star charts?