Keep in mind that in casual mode you can get hints to help you solve your quests by clicking on the quests in your quests journal (book icon, bottom left of your window). You can get several hints for each quest. Keep clicking on the hints list until no new hints appear.
In hardcore mode, you will get the option to inspect or interact with an item when you click on it. In casual mode, clicking an object will immediately give you the information or action you need.
The question mark icon in the bottom right of the screen will show you all exits and all clickable objects.
Pay attention to what everyone says, for - more often than not - you'll find a clue in the dialogue to point you in the right direction.
Diaries and other written material can be read by examining them in the item menu. They're usually full of clues.
If you're stuck, try looking again at the items in your inventory. You might have missed a combination that will move you on to the next part of the story.