Paleo-paganism (Ancient Greece)
In Ancient Greece pagans used mainly human sucrifices to show their respect. Since Ancient Greeks valued human life greatly it was considered a big sucrifice. When it came to human sucrifices they usually picked a king's daughter or wife. Moreover in ancient Greece they used to sucrifice animals for smaller requests.
Neo pagans usually worship their Gods and Godesses by sucrifising something that has great value to them or is expensive in general. However I would reccomend to burn something in your ritual that has great value to you and simply pray it could be anything as soon as it's not alive.
For Zeus you should also use incence (I would reccomend basil and laurel) and always keep something metal in your altar.
In general however Greek Gods appreciate sucrificies.
Moreover if you pray in Greek or ancient Greek it will also be apreciated.