This is a game of logic, observation, and chartered accountancy.
Some clues are visual; some clues are audible.
Solutions can be slightly different from one game to the next; but...
It's possible to play the game perfectly each time, without guessing.
Some tasks can be done in more than one way - find the cheapest.
Some items are useless, but some apparently useless items aren't.
Some items are useful, but some apparently useful items are red herrings.
Some items are hidden, or behave differently depending on the 'game state'.
Keep asking "What is that for?" or "Why did that happen?"
If something odd happens, try it again in a new game where it can't happen.
If you get 666 points on the high score list by cheating, you still win.