I think the star chart depends on how you want to do it. Personally I didn't bother with the chart because DS didn't seem very interested in the notion, he just liked the stickers. So he got a star sticker for every wee that went in the potty, and a special more exciting kind of sticker for every poo and he stuck them in various places like his tee-shirt, or the fridge, or on his potty or whatever!
Then instead of saying "do you want to do a wee" I would say "do you want to earn a sticker?" which got a positive response more often. I would often give a sticker just for trying even if no wee came, because he was quite reluctant to sit on the potty at first.
One friend gave her DD a little book and each page was a day, she stuck stars on that day for each wee or poo. this had the advantage of being quite portable so she was able to take it to nursery and they carried on there.
Another friend had a star chart with a column for wees, a column for managing his own pants and trousers, a column for poos, and a column for going a whole day without an accident. There was a different kind of sticker for every column.
Another friend just had a blank piece of card she stuck on the fridge and the stars just accumulated and it got more and more starry - no particular system.
And another friend had a column system of ticks working towards a reward after so many wees/poos. I can't remember what the reward was - a toy I think.
So lots of possibilities - I think you just have to tailor it to your child. If they like the idea of storing up points then perhaps the reward kind is the way to go - DS is more of an instant gratification kind of boy so stickers were popular with him and he wasn't bothered about keeping them, or counting them up over time.