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Rather a shitter myself, but I've recently been getting into competitive, and it's really not all THAT complicated. I favor Smogon's Underused tier, myself. It really just boils down to knowledge, honestly. Knowing what Pokemon can do what, and what TEND to do what. Knowing what can take what hits, knowing what can't. Thinking about possible held items, switches, etc. It all comes with experience. You'll get outpredicted like a motherfucker for a while, but you start to get a feel for how people play, and then you start making your own outpredictions. Feels fucking great.
Also, get a Heracross. This is good advice for anyone.