Hi! Is there something I have to look at when starting a new iOS App? For example resolution…?
Thanks 
Google is your friend; this isn’t Unity specific here.
iPhone5: 1136x640
iPhone4/S: 960x640
iPhone3GS: 480x320
iPad2/Mini: 1024x768
iPad3: 2048x1536
Regading the placement of GUI elements and stuff, you should use a layout that anchors your GUI to appropriate areas of the screen, such as the corners.