I think one thing that really opens up opportunities for completing dex, getting rare pokemon, event pokemon, shiny or competitive pokemon is the event Pokeball Vivillon. People are trading lots for them, and they are becoming more and more easy to get a hold of as people clone them and make more. From the look of it, most of the ones I've had and traded have been clones or clones of clones of two different ones, one Timid, and one Gentle. There are others out there, but it doesn't really matter I suppose. Its a cool event pokemon to get a hold of and use for your collection or trade away for something cool.
Now after getting the majority of the stuff I was after from trading, I've been working on breeding 5IV pokemon with the correct natures and egg moves if possible. When I first stopped playing back a few months ago, I had trained a 5IV Timid, hidden ability Drought Vulpix, and had almost got the correct 5IVs on a hidden ability Huge Power Marill with Belly Drum and Aqua Jet egg moves bred onto it. That thing is a bit more complicated to breed, with a few more stages, but in X and Y, breeding and training is a lot more simple now than it was in previous generations. Its used quite a lot in competitive battle, with Adamant nature, Huge Power and Belly Drum working together to give it ridiculous attack, and then add in the fact that he has priority with Aqua Jet, and good coverage against other pokemon that wall it quite well, Play Rough and Superpower offer Fairy and Fighting attacks respectively.
Some cool visual guides for breeding IVs in the 6th gen games: Link | Link
I also managed to get a 6IV Ditto (they are hacked or RNG'd or something, but I didn't know this at the time. In fact, I kind of got ripped off, as I traded an event Celebi for one, whereas the Dittos are being given away over at this subreddit) Anyway, this is quite helpful for speeding up part of the breeding process. I managed to breed some more stuff over the past few days, including 5IV Modest Scatterbugs, 5IV Adamant Honedges and some more.
When it comes time to train EVs, it is now easier than ever. Gamefreak keeps making the competitive side less murky and mysterious, more accessible and easy to get into. Which is really cool. Now, you have the Super Training side of things, where minigames help you quickly train Pokemon in certain stats to achieve the full potential. I actually only found out about this today, I knew it was there, but only tried it out for the first time. I was trying to get Reset bags for resetting the EVs to zero. Apparantely they are pretty rare though, which sucks, as I may or may not be correct in saying that there are no EV-reducing berries now. There is also Pokerus, Macho Brace, and even better, the Power Items. Check these links for more information, but basically you want to combine horde battles, pokerus and the relevant power items to EV train quickly. VERY quickly. It can be done in 15 minutes, maybe even less.
Theres a lot to get into in pokemon, comment if you have any questions or with your experience with the competitive side of Pokemon.
Smogon guide to EV training in hordes
Marilland guide to EV training in hordes
I had some quite useful posts back a few months ago, and with the aim of compiling them all and keeping them easy to find, I've added Pokemon and Pokemon X tags, but here are the links as well;
This has some relevant links if you want to go hunting shinies
This has a lot more, and some good breeding links
