Considering the ever-expanding nature of the CLAMP universe, there are really only two good strategies in my mind for attacking their interwoven literary behemoth: starting right at the core with Tsubasa RESERVoir CHRoNiCLE, or by taking on all the mostly independent stuff first. Sure, whether you watch Tsubasa first or Card Captor Sakura first you'll have to meet the eternal protagonists Sakura and Syaoran pretty quickly, but the latter lets them exist independent of anything but their magic antics and elementary school life. The problem is that a lot of the other CLAMP works don't have such a nice boundary, in particular because the Tsubasa crew dip through so many universes on their journey, perhaps the most recognizable being the supernatural wish-granting shop of xxxHOLiC, the first jump in the Tsubasa story and a stark tale of compensation and maintaining balance in the universe, even with the omnipotence of their service.
If that sounds serious, the taste of it we get in Tsubasa is pretty heavy in tone and outcome, condensing Fullmetal Alchemist's equivalent exchange mechanic into one impactful scene, but xxxHOLiC is a comedy built on all that philosophy, or rather on the lives of the wishmakers who keep it going. In fact when the shop owner Yuuko is doing business with the people or spirits who accidentally wander into her shop, isolated in time and space yet conveniently located in downtown Tokyo, it stands in stark contrast to how she makes her assistant Kimihiro Watanuki jump through all sorts of unnecessary hoops to actually keep the shop in business. Mostly because Yuuko's definition of keeping things in business is making sure she has a steady supply of food and booze, although for all her hangovers it's clearly a service that lets her appear gravely professional with her clients, so who are we to judge?
Watanuki is the classic sort of unwitting participant in this new world of spiritual manipulation, the same sort of disgruntled but ultimately excited and kind grunt worker as Renton Thurston in Eureka Seven. He was gang-pressed into service as compensation for Yuuko keeping a particularly nasty spirit off his back, even if being bullied by Yuuko and the various spirits she uses to run the shop seems like too high a price. He's an honest narrator, barely hiding his enjoyment of everything about this job and how it allows him to be honest and open about seeing spirits, a source of trauma for him as a kid, as well as his crush on his classmate Himawari and his fake hatred for their mutual friend Doumeki. Himawari is cute, cheerful, and blissfully unaware of the world of spirits, while Doumeki is blunt with a monotonic voice that belies him caring about his friends, which manifests in him being a strong ward against spirits due to years of the sacred art of kyuudo. Their high school antics blend into whatever the job of the week is for Yuuko's shop, making sure everything stays light.
The most recognizable thing of any CLAMP work is the character design, almost unbelievably lanky with ridiculous facial expressions, but there's also the matter of director Mizushima Tsutomu being at the reins. Mizushima manages to strike a balance between comedy and technical jargon in many of his best works, such as Joshiraku, Genshiken, Shirobako, and Girls und Panzer, as well as doing overblown dramatic tension in Another and The Lost Village, but he stays away from making the world of spirits very technical in favor of simple objectives in each story, and he stays away from drama and bloody murder but occasionally captures an ominous foreboding sense of a larger unseen world, less sinister as just unforgiving. A beach episode captures this comedy with all the usual antics, but the plot of a woman haunting their cabin hits on both the funny character interactions and the inherent mystery in xxxHOLiC's earth.
Also despite being part of the CLAMP universe, only the Shunraiki OVA makes the connection with the Tsubasa story, while the rest can definitely be enjoyed without any prior knowledge. In the usual form of such episodic shows there are few “plot developments” per se, although watching the episodes completely out of order will make the role of some of the recurring characters unclear. Once all the characters are established, the two full-length xxxHOLiC series' can be watched at random with pretty much no impact. As always with that sort of show, it can be hard to watch too much at once, even with the solid variety that the stories display. But it's nice to have the structure of the jobs, the comedy of the character pool, and most of all the foundation of compensation and wish-granting to create both a moral message and an atmosphere in and of itself.