The most distinguishing factor of Joker's appearance is that you don't get to see his face completely. Though there are times that he shows one of his eyes, most of the times half of his face is covered with his headpiece, cap, beanie or his hair.
The first time we get to meet Joker in the Ura Butou Satsujin, he is dressed similarly to a jester with a half black and half white puffy pants, a white chest piece with the spades symbol and black and white stripped puffed sleeves, a matching half black and half white pointy headpiece and a pair of black and white gloves. On top of his jester pants is a skirt-like attire that is made up of alternating strips of black and white cloth. And to finish it off, he has a plain white mantle that reaches his heels. As for his hair, it's braided into three long strips starting from the nape. Even before the Ura Butou Satsujin, and even before he was part of the Uruha Jyuushinshu, he was already sporting this attire of his.
After a couple of volumes, we see him change appearance. Though he still braids his hair in three long strips, instead of his jester headpiece, we see him wearing a baseball cap that still acts as a cover for his eyes. And instead of his jester battle costume, we see him wearing a white shirt and cropped shorts. Over his shirt, he wears a black open vest with a patch stitched on it's right breast area. He wears a watch on his left wrist. After the Sealed Land arc, when we meet him with Kurei in Kurei's mom, Tsukino's house, waiting for Raiha, we see that he's still wearing the same cap and a plain white shirt. The only difference this time is that he ditched the black vest, he's now wearing couple of beaded necklaces and his hair is braided into four stips instead of his usual three.
For the last time that we see him, during the SODOM arc, Joker's hair is now blonde and he wears it loose. And instead of a cap, he now wears a beanie. In the manga illustrations, he wears a dark tank top with a light colored baggy pants and black shoes. He's wearing a necklace with a gear-like pendant, a chain hooked from his back to his front left pants pocket, a black wristband and a bracelet at his right arm, a ring (or two) at his right middle finger, another one at his left index finger and an earring at his left ear (though if there's one at his right, it's hard to tell). In the PS2 game, Flame of Recca FINAL BURNING, it was shown that he was wearing a violet tank top and beanie.