Clerks was a decent amateur comedy, and while nobody in the movie was a particularly good actor, Smith did find enough talent to avoid making a total botch of his first effort. Clerks is still an uneven film that hasn't aged well and tends to drift unless Anderson and O'Halloran are onscreen together. Stil it was a promising first film. Except, well, what has all that promise come to in the years since.
His later movies are more "polished" only because Smith had a small army of professionals helping him as well as vastly larger budgets, but Smith has really learned nothing about directing in over twenty years and if he hadn't gotten lucky during the indie film boom back in the 1990s he would still be a nobody.
Instead, as a film maker he's become lazy and self-referential, and also channeled all of his terrible instincts into other media, like comics and more recently, animation.