There was something I read while ago about how to make good decisions.
A few years ago someone told me that being a good decision maker, being assertive and decisive requires having a decision making paradigm.  This person’s rule was, if I have a choice between doing something or not doing something, always do it.
Should I go out tonight, or stay in?  –> go out.
Should I buy this shirt or not? -> buy it.
It occurred to me that there were some limits to what this particular paradigm could decide.  But still, I realized that having this kind of decision making process would help me out with all those “what should I do tonight” questions, that pop up on a daily basis.  Being able to quickly answer questions, definitely improves quality of life.
More recently however, I’ve come across a far better decision making paradigm. 
If I have a list of the goals in my life.  Then a decision which is in line with those goals is by definition a good decision.  Any decision that doesn’t agree with my goals is not a sound decision.  So, today when I went to McDonald’s for lunch, that was a bad decision, because 1. I’m trying to save my money, and 2. I’m trying to stay fit.  The good decision would have been to make a salad this morning, and bring it in to work.
With this new perspective, it’s easy to evaluate everything I do.  And it’s easy to be decisive when I need to be. 
To be a good decision maker then, you need to have a list of well defined goals.  Once you have that list, you need to keep it mind every time you have a decision to make.  With practice, it will become intuitive, and the more you review your own decisions, over time you’ll be making less poor ones and more good ones.