The easiest way to become more decisive is to follow a well known assertiveness training technique called "The 4D’s." This can be used at home, work or study regarding an issue that you have to make a decision about.
The 4 D’s stand for:
Adopting this approach enables you to decide what to do about something really fast. It kills procrastination and any delays in decision making. Choose what you want to do, by using 1 of the 4 techniques.