How to deal with riddler trophies
Some of the things you have to do for the riddles are pretty convoluted, so if you come across a specific riddle, it may be better just to ask about that one.
Solving Pressure Pad Riddles: I only recently figured this out myself after around 30+ hours of play. What you need to do is step on the pads to activate them without touching the ground or anything else. There's nothing you can pick up to place on the pads, and using Explosive Gel or any other tool won't trigger them.
Often, the order doesn't explicitly matter, however, there's usually a manner which is most efficient or that you need to do in order to complete it, even though it's not stated in game (like one where you have to glide back and forth between some buildings, rebounding off the sides).
If you miss a pad, they will all reset and you have to start over. What you need to do to activate them without hitting the ground varies per riddle, but I have found that the Line Launcher and its upgrade, the Line Launcher Tightrope are pretty helpful with these.
Solving the Riddle with the questions marks on the ceiling: What you need to notice for this one is that you can't hit all 3 at once with your Quickfire Batarangs. The third one (the one farthest from you) won't be targeted. You need to hit that one with a Remote Control Batarang either before or after you hit the first two with your Quickfire. Make sure you do this within the time limit!
IGN has a video where they do this. The cut starts after they've already Quickfire triggered the first two Question Marks.
Pressure Plates work by only sensing Batman/Catwoman on them and then detecting whether or not their next "surface touch" is a pressure plate or the ground/wall (ceilings are cool for Catwoman). As long as the next thing you touch is a pressure plate, they will stay on. You can do this once Batman gets the line launcher, stand on a plate, glide or move on the line launcher to the next plate until you have them all. For the ones on the walls, you need to glide to them, then glide to the next and so on. You more or less need the grapnel boost so you can keep regaining height for your glides.
Riddler mines keep resupplying themselves. But the trick is that you don't always need the mine disruptor to get the trophy. In 1 or 2 of the mazes Batman can actually go around the mines. Go ahead and experiment to see which ones those are.
? Switches: The one in the railroad car requires you to hit several ? switches on the ceilings. For those kinds of timed ? switch puzzles, you can try quick throwing a batarang at the first one and then using the remote batarang to hit the others. It's a matter of timing and practice after that. When you do them, throw the remote at the farthest one first and work your way back towards Batman.