Usually a feeling of uncertainty in your choice appears in people who in childhood were deprived of the right of choice. They completely suppressed the authority of the parents and their word was for a child last.
First, you need to learn to understand what you like and really need. In the restaurant, in a cafe just select the meals that you love and want to try, and not one that is cheaper or easier. In store purchase that dress like and think fits you perfectly, and not what I advise you mother, girlfriend or designer of a fashion magazine.
Most importantly, do not be afraid to take risks, it will help you to learn how to make decisions. In the most difficult time, if you are confused, panicked, put yourself in the place of the authoritative man for himself and try to look at the situation from his point of view.
Always look for the pros and profit, and not think about the disadvantages and losses when making any decision. Imagine some situation from the past life in which you failed to make your own clear decision, but you listened to other people's opinions and stopped to watch, for example, reality shows. Try to analyze the development of events if you have taken more, the opposite decision. What would change and in what direction?
And finally, learn to act up, tap into a child that will always require what they need and try to get it. Even in childhood, your wishes and decisions not allowed to be, but now you are not constrained by boundaries and limits, so why not take advantage and learn to make decisions.