Presuming of course that the question is what is my strategy in-game, since in-game battling and competitive battling are two entirely different things...
In-game, I rely on type advantage and relatively balanced pokemon. Trying to sweep in-game isn't necessary, and I don't even think it's sound strategy. There's no reason to waste a moveslot on a coverage move that's not going to KO the opponent anyway, since all that means is that you'll maybe chip away at the opponent a bit before it KOs your pokemon, when you could've just switched in something with a super-effective STAB and been done with it. Since the AI is dumb as a bag of rocks, switching is pretty much risk-free.
So I go for pokemon who are bulky enough to take a hit on the switch and then either bulky enough to take yet another hit before they get off their attack, or fast enough to get in the first hit on the next turn, and I carefully balance types so that I've got at least a couple of things that can potentially handle pretty much anything that shows up. With the right pokemon, I can be pretty sure to always have at least one SE STAB to use on pretty much anything that pops up, and with well-trained, beneficial nature pokemon (which mine always are), a good SE STAB is almost always a OHKO anyway, so that's pretty much that. Then when the next thing comes in (I always play on Set, so I don't know what's coming next), if necessary, I just switch to whatever has the SE STAB I need.
And to that end, I very rarely use fixed teams from beginning to end. I generally work out of a pool of viable pokemon and rearrange my team to suit whatever it is that I'm doing at the moment. I use a balanced team if I'm going along a new route and am going to be facing a lot of different stuff, but there's no reason to take an Electric into the Ground gym (for instance), so I generally don't.
The only real exception to part of that is the E4. Since there's a limited set of types, type advantage is even more important and easier to make sure you have, but since they have sets of powerful pokemon, it pays to treat it more like competitive sweeping, with a bit of setup first, so whoever is handling a given trainer's pokemon can fight three or four or five of them in a row. And since the Champion (and/or the "guest," like Ghetsis) is going to be using a very tough team, it pays to have a wall of some sort, so you've got someone to switch in and let sit for a while, so you can work on reviving/healing the rest of your team. Other than that though, it's the same basic strategy - type coverage, well trained pokemon with beneficial natures, bulky enough to take at least a hit or two and/or fast enough to outspeed them, and the best STAB moves available.