How to complete side missions on Batman Arkham City?

I finished Arkham City story mode but not side missions. Only have 40% shot in the dark, 20% watcher in the wings, 30% enigma conundrum, 0% identity theft done. And right now there's nothing to do but look for riddler trophies, how do I finish these missions? Been running around forever there not coming up.How to complete side missions on Batman Arkham City?
As you get more and more trophies, you will be given hints to proceed with the missions. You must regularly check the map for any new marking. In the watcher mission, always use detective mode and try to find a guy standing in the top of a building alone. I remember one of the places he was standing is on the giant wheel.There are four places in total out of which you found only one yet. I guess you have not solved enough of riddler's challenges, that's why nothing is coming up.