So from reading the Player's Handbook, it seems that the Ready action is taken instead of any other action as it is an action in its own right. However, can you move on the same turn that you ready an action? For instance, (taking the example from the Player's Handbook):
If the cultist steps on the trapdoor, I’ll pull the lever that opens it
Presumably, when you ready this action, you would want to move near to the lever so you can pull it when the time is right. Likewise, with readying a spell, you would obviously want to move away from combat so you could concentrate on the spell.
Secondly, when the trigger goes off do you have to wait for your turn, or do you in effect get a bonus turn? For instance, the cultist starts running towards you, but on his way he steps on the trap door - so you immediately pull the lever, even though it wasn't your turn. I assume you then act as normal when your actual turn comes around?