Don't bite off more than you can chew (貪多嚼不爛 )

1)to try to do more than you are able to do.

eg. Don't bite off more than you can chew. Let someone else organize the party.

(2)to try to do something that is too big or difficult to do.

eg. The key to success lies in not biting off more than you can chew.

go/sell like hot cakes (賣得很好；暢銷大賣)

go/sell like hot cakes ---if things are going like hot cakes, people are buying a lot of them very fast. (賣得很好；暢銷大賣)

eg. The book has only just been published and copies are already selling like hot cakes in both Britain and America.