At the beginning of the game when you first come across a little sister, rescue her. And then in the next mission when you get the opportunity to come across more, make sure you rescue them all. You will receive a gift on the second mission in a teddy bear. One of the gifts is a plasmid to hypnotise Big Daddies. It's important you have this as it will become a lot easier to go through the game using this plasmid. Just make sure you have the space for it, and make sure you use it wisely whenever you come across a Big Daddy.
This procedure requires editing one of the .INI files, which I will talk you through but when you find it. Right click on it and copy then click somewhere safe in your computer and paste. This will be your only warning to do so
The cheat gives you access to god mode, fly mode, no clipping, teleportation and a mode to disable fly mode or no clipping.
Right, first locate your Bioshock folder. The default install of this is C:/Program Files/2K Games/Bioshock (Drive letter maybe different if you installed it to another drive)
Now go to the build folder and then release folder. In here is the defuser.ini (remember to copy & paste). Now double click on it to open the file in Notepad.
Scroll down until you find the keyboard keys listed, some will be blank and others will actions beside them. These are in fact your controls and hotkeys for the game.
All you do is simple. You type god for godmode next to the key you want to activate it on. fly for fly mode against a different key. ghost for no clipping. walk for the disable mode and teleport for teleportation (this will take you to your pointer)
If that isn't clear then here is an example:
You will have to activate the ones you want at every new scene/cutscene I'm afraid but it does help for gaining great screenshots
Now save the file and load up the game. You may have to customise your controls again however