Hitman: Absolution is not linear, thus there are different paths leading to subsequent areas. You can also get rid of main mission targets in different ways. In order to find different variants of behavior you might use your Instinct. If you play on Easy or Medium difficulty level, the game will occasionally show hints after activating Instinct (screen above). On higher difficulty levels hints are not available, but anyway you should use Instinct to locate interactive items and devices more quickly.
Every time you reach a new location, it would be good to spend some time on getting familiar with it. These preparations are primarily aimed at finding all possible passages and in that case I recommend to look for places which are not guarded (a good example would be ventilation shafts or buildings cornices). Getting familiar with given location may also be helpful in determining the hostile characters paths or marking places which are not accessible by default and require stealth actions or usage of the proper disguise.