I don't think there's any set way to do these things.
Find what fits in with your house and your kids and what's going on in your world.

But just to give you a few ideas.
If you wanted to do a weekly chart and if you can afford rewards every week then that's great, go for it.
If it ran from say Mon to Friday or which ever day you chose to end it on, and the child only had one box left to go. Grab a sticky note, put a smiley face in green or any another colour that is different in the last box, and write on the sticky note "An extra smile for doing one (state which ever one) of your jobs extremely well, so here's a free smiley"
Make something up something like, "here's a free smiley for simply saying thanks or putting your bag in a great place or your shoes etc etc".

It really can be what you want it to be, but the more positive fun stuff you do, may result in having to start doing daily rewards.