There's a quote in the Dhammapada that I think is more clear than the "four noble truths" (which get too much emphasis):

Avoid all evil, cultivate the good, purify your mind: this sums up the teaching of the Buddhas. (183)

Matching what you said, many religions (and non-religious people) emphasize avoiding evil and cultivating good, but the practice of purifying your mind is quite good.