How do the Five Precepts, Eightfold Path, and Four Noble Truths help a Buddhist live a better life?

All three principles mentioned in the question, help a person to live a better life by improving their intentional actions (kamma).

When one stops killing living beings, for example, one can expect a better return karmically. By giving freedom from fear to an unlimited number of beings, we ourselves can be expected to receive a corresponding unlimited amount of freedom from fear, karmically. 'What goes around, comes around'.

Thus discipline / restraint in an ethical sense, has rich rewards, the Buddha seems to have said.

Refraining from killing is the first of the five precepts.

More on these here:

http://www.accesstoinsight.org/ptf/dhamma/sila/pan...

http://www.accesstoinsight.org/ptf/dhamma/sila/ind...