9Kplus1
Smash Master
Play a lot and lose to as many players as you can. One very important aspect of competitive Pokemon is planning ahead (interpret that however you'd like, but I'm referring to mid-match) and without a strong knowledge of the current metagame--which Pokemon / cores are dominant, and what players are doing to adapt--that's going to be hard to do. With that knowledge in mind, you'll be able to more effectively analyze situations and develop a plan to gain (or regain!) momentum. Moreover, I've seen quite a few players halt their own progress by obsessing over their [few] wins. It's healthy to give yourself a pat on the back every now and then, but if you'd like to actually be good at Pokemon, always maintain an open, hungry mind.
Lastly, don't be intimidated by the community. The second you make an account on any competitive Pokemon site, take a gander at what's considered to be, at least, acceptable posting, and get to chattin! You won't be able to learn this game via lurking -3-
I personally think that this is good advice if you want to quickly gain some momentum in picking up competitive Pokemon. However, a roadblock that can come with this option is analyzing how the team is [to be] used; simply put, because the team is not a creation of your own, you likely won't feel comfortable with [using] it and could miss the entire premise.
Ehhhh, this is probably the elitist-tourney-wannabe-prick in me talking, but I prefer PO for the competitive experience. The PO community is much less populated, but that only makes it more likely to run into a smart player; seriously, I've lost count of how many times I'd won a ladder match by some random just... playing badly. I've yet to run into a PO player who, despite having a Nattorei, Lando-T, and Rotom-W available, leaves their Mega Luke in on a 95% Hippowdon and SD's (yeah, misclicks are a thing, but situations like these are commonplace among high- and low-ranked ladder players alike 9.9) of all things.
Eh, you can make that argument for every top offensivemon. Specs Keldeo does well with Sticky Web support; Azumarill and Mega Mawile work especially well with Stick Web support; every Dragon Dancer is much harder to revenge kill with Sticky Web support (imo, their expansive movepools are comparable to PuP, as they all can easily force switches and use that opportunity to set up). Similarly, it's possible to argue that paralysis support is just as good as a result of Sticky Web's poor distribution and the high utility of Rapid Spin / Defog. Mega Kangaskhan's biggest weakness is being either too slow or too weak before Mega Evolving; the opposition has a much easier time locking down Kangaskhan's available options and pressuring it. As I'd mentioned, planning ahead is a very important part of Pokemon. Don't give Mega Kangaskhan the opportunity to get too much momentum, and it won't be much of a problem.
We're still in this 'shiny new thing' phase, in which the general opinion for now is that things such as Talonflame and Greninja are "top tier". There just hasn't been enough time for players to adapt to the thought of another strong threat. Remember the good ol' days, when people were genuinely willing to suspect things like Dragonite and Rankurusu? While Mega Kangaskhan plays much differently than the two, it's being handled by the community in pretty much the same way.
Oh yeah and SupportKang is pretty nice. My only concern with it is how easy it is to wear down; the Protect nerf (ironically) makes Kangaskhan a liability when pit against stall and smart offense players, not to mention how susceptible Kangaskhan is to status -3-. Anyway, as I'd said, it's not too hard to pressure Mega Kang, and that set is no exception.
