Antonyms for the phrase "lay on thick" include phrases such as "speak plainly" and "be honest." When someone lays on thick, they are typically exaggerating or being insincere in their flattery or praise. Being honest and straightforward, without embellishing or exaggerating, is a good way to avoid laying it on too thick. Other antonyms for this phrase include "be subtle," "show restraint," and "use tact." These phrases all suggest that rather than being overly effusive or sentimental, it's better to be measured and even-handed in one's approach to communication.