I've found the first four books of the New Testament to be a very valuable guide to approaching life no matter who wrote them, as good as anything else ever written, and following the advice therein is a definite path to happiness or contentment or whatever one's soul is searching for. The Old Testament has some gems scattered throughout but you gotta get through the slaughtering, adultery and all the good soap opera stuff to find it.

But - and not saying this just to debate or piss off anybody - one can also find equally good advice in the Dharma of Buddha and Taoist works as well, plus works of the stoic philosophers Marcus Aurelius and Epictetus. Heck, a fellow could do a lot worse than just reading Tolstoy's short stories. There are lots of others but these examples are among the ones I'm most familiar with.

Gunnery, gunnery, gunnery.
Hit the target, all else is twaddle!