I don't know what type of idioms I would put in a paper like this. Please help.
I'm not sure there's enough information here to reliably answer the question. I'm not sure what you mean by "cause and effect paper"- this sounds like a type of paper that means something to your class and you teacher, but it doesn't necessarily mean anything to someone writing online. As such, I'm not really sure what the purpose of your paper is.
This makes things difficult, because the purpose of your paper determines what idioms would be most useful for your paper. Are you trying to show the effects that smoking has on the human body? Are you trying to explain what causes people to smoke? Without more information, it's difficult to give you an answer.
My advice would be to visit http://www.idiomsite.com and find an idiom that you can use in one of your sentences. You never know- you may already have an idiom in there, and not realize it! If you're still having trouble, try asking your teacher for more help.