Hitman (World of Assassination Trilogy)

If you have instinct mode on there will be a dot over people's heads that will see through your disguise.

A surprising amount of assassinations can be pulled off with patience and choking/neck breaking at the right time. This is often boring but sometimes the opportunity will fall into your lap.

Experimentation is good, doing levels over again and completing more challenges unlocks more tools, weapons, starting points, etc

There's a gadget that's a phone bomb, you drop it, someone picks it up, you dial it, and when they answer it explodes, has a small range but can take out like anyone standing next to the person with the phone, but the important part is you have to take into account that it takes like 3~5 seconds for them to answer the phone once you trigger it...yes this fucked me over on an Elusive target once, why do you ask?

The game autosaves frequently and that can be a life saver--but as was mentioned it's a good idea to make a manual save before you try something that seems risky.

Steal every tool, knife, can, soda, fruit, etc that you can. Many innocuous objects are actually keys to opportunities or interactions around the map.

Game Modes

Contracts mode is user created stuff, it can be pretty fun, you can also make your own fairly easily

Escalation mode is just the same short mission over and over with it upping the ante each time like with additional targets, conditions (no non-target kills, hide bodies within a time limit, etc), or obstacles.

There's a console-exclusive set of missions called the Sarajevo Six that's basically an additional target in each level. The game recommends doing them after playing through and in order, mostly to avoid spoiling plot stuff. Watch out: the fifth is very difficult.

Elusive Targets: you are locked in once one target is dead or one objective is completed. Before this point, you can restart! Take advantage of this to learn the mission. Be absolutely certain before you pull the trigger!

Pro mode is unlocked after you've developed some mastery in a given main story episode. It's much, much harder than the main game, with new guards, cameras, mechanics, and combat is almost instantly lethal. The big change, though, is that players only have one save per run on Professional- and you must complete the mission to complete each challenge and gain Pro mission mastery and unlocks. Pro mode's rewards are 99% cosmetic, and are thus best left for after you've truly mastered the rest of the game.