There are numerous riddler challenges in Batman: Arkham City. Some of the riddler trophies are caged and you have to open the cage by activating the related mechanism. 

For example, there are multiple riddler pressure pads which should be pressed simultaneously to get the cage opened. How can I do that? Should I look for materials around to be placed on those pressure pads? What equipment should I use to gain those trophies?

As an another example, I found some green question marks at the ceiling of a railroad car in the subway. By using the detective mode, I could see there are some wires connected to the question marks which end at some point. I tried throwing batarangs on them but no go. 

Can you give me some tactics on how to deal with these riddles?