EDIT: I could probably use some help getting into this tier; I'd appreciate it if anyone can give me some tips. Thanks!
Alright, so now for some actual advice:
When starting out in a tier, you need to identify how it functions, common strategies that are used, and what works, and then teambuild accordingly; afterwards, it just depends on your skill level of using your team and how good you are at predicting. In XY UU, offense is the face of the metagame, and Pokemon such as Kyurem-B, Latias, and Keldeo are ruling teams. Rain teams are also very common and extremely dangerous, with Politoed's Drizzle ability and Swift Swim users such as Kingdra, Kabutops, and Ludicolo ready to abuse it. Rain teams also have some overpowered threats that utilize different tactics such as Thundurus-T and Tornadus-T to abuse the weather. Offensive tanks such as Florges are also common, as they're stops to dangerous Pokemon such as Latias. Dark is currently the best typing to have in UU, which explains the popularity of Pokemon such as Bisharp and Krookodile and Pokemon that can check them such as Mega Heracross (normal Heracross also works to an extent).
So now that you have a brief idea of what works and what doesn't, you need to start teambuilding with a goal in mind, preferably have your team based around a late-game sweeper or a team style. I'll share what my most recent team was based around: Nasty Plot Thundurus-T. With that in mind, you need to pick partners that will help that sweeper by either giving it opportunities to set up or weakening things that wall it. In this case, Mega Blastoise was my pick, since it attracts Electric- and Grass-type moves, both of which Thundurus-T can switch into. Blastoise also got rid of Weavile, a rather troubling Pokemon for Thundurus-T to deal with if it's at low health. As I mentioned in my previous post, Roserade deals with this core fairly well if hazards are on the fields, as Thundurus-T cant hit it hard while Blastoise is 2HKOed (OHKOed more often than not with hazards). So my next choice would be Escavalier, which is a complete stop to Roserade and also gets rid of Pokemon such as Kyurem-B and Latias, the former of which can take a hit from Thundurus-T and OHKO it with Draco Meteor. Furthermore, Escavalier also gets rid of Choice Scarves with Knock Off, so they won't revenge kill Thundurus-T when it tries to sweep. After that, I would probably have a hazard setter like Nidoqueen, as it also deals with Pokemon such as Mega Heracross and Toxicroak and provides a switch-in to Rock-type moves that threaten Thundurus-T. Then, there should be a somewhat defensively-oriented Pokemon that can take on the likes of at least two DrizzleSwim mons well, and then a Choice Scarf/priority user of my own to revenge kill stuff. This is just an example team that I haven't really laddered with too much, so don't just c/p it, instead use it as an example of sorts. Also remember, you don't need to finalize everything on the first try, ladder with your team a bit, and if you see some holes, try to fix them.
I don't know how helpful or "correct" my advice is, so take it with a grain of salt :) Regardless, I hope I helped ^.^
I'm surprised at Crawdaunt, but not surprised that a gimmick sweeper is getting more usage than utility mons
Crawdaunt is actually a pretty good Pokemon, due to it having a Dark typing, which automatically makes stuff great this gen since they get STAB Knock Off. Furthermore, Crawdaunt has a high base 120 Attack, which is further complimented by a STAB priority in Aqua Jet. However, it is fairly frail, especially on the special side, and its low Speed is also a pain to deal with when Aqua Jet isn't strong enough. Due to these reasons, Crawdaunt might not end up UU, but rest assured, it has a cool niche :]