If advice, criticism, or actions are constructive, they are useful and intended to help or improve something.

She criticized my writing, but in a way that was very constructive. 她批评了我的作品，但是以一种非常建设性的方式——我受益匪浅。

If you don't have anything constructive to say, it's better to say nothing. 要是你没什么有用的话要说，最好保持安静。