>>23357334I made the same mistakes when I first started wifi battling, 6 offensive pokemon with no defensive or utility mons. Takes awhile to figure out whats going on. Go to
http://www.smogon.com/dex/xy/pokemon/ look up pokemon you want to use or are fond of and figure out what to invest (EVs and natures and items) in for each pokemon, and also some sample move sets to teach each pokemon. Look at defensive pokemons and find at least one that you like. Other than water types, there are mons like Blissey/Chansey and Umbreon that serve well as walls. Try to make sure no one type can sweep your team.
To start building your team, figure out what your "win condition" will be, usually this is a Mega evolution that can deal severe damage and "win" the match for you, but some people also go for more defensive teams that have an attrition "win condition". Once you figure out your win condition, figure out how to best set-up and compliment your win condition and go from there.
For example, I build offensive teams, so my win conditions revolve around either my M-Lopunny or M-Gardevoir sweeping the opponent. In my last game I brought M-Lopunny, she is very fast but her ATK isn't very high and her type coverage is small, so prior damage on enemy pokemon, removal of threats to M-Loppuny's safety, and breaking through enemy walls are the job of my other mons, then Lopunny could come in and wreck some shit up. Sticky Webs slows your team down to allow my slow but very strong wall breakers Scizor and Nidoking to blast through enemy mons, Stealth Rocks is some very minor chip damage, and Skarmory and Milotic are Defensive pokemons to deal chip damage and whittle away at your team. Sticky Webs is very important, so I put Galvantula as my lead with a focus sash to ensure he will always get Sticky Webs out (except against taunt, magic bounce, etc). All this is so that my win condition pokemons can slap some shit.