Many players will often assume that the most amount of damage is the ultimate factor in who wins, however that is not the case at all. This is why various status moves exist, to shift the advantage. Also many abilities can do this, like prankster or gale wings to take the speed advantage. There are a lot of moves and abilities that are overlooked though, because they offer no obvious advantage.
Luck based tactics can be very effective, but require the correct setups to work at all. Instant KO moves have very low chances of success, they are luck based. but with the correct build, a highly defensive pokemon that has defensive boosts, for example, will benefit the luck based tactic, offering you a lot of chances to use the high risk moves. But if you fail to build the pokemon correctly, you will fail.
Defensive tactics are overlooked a lot, turning everything into glass cannons. Sure, the glass cannon may be capable of sweeping another glass cannon who has lower speed, but you will lose that glass cannon. If your opponent is smart, you will lose that cannon quickly. Mega Kangaskhan is the perfect example of something many players turn into a glass cannon, my Sableye scoffs at those using foul play to bring them down.
So when you boost up the offensive ability, you lose out on a massive tank. Mega Kangas should be utilized as a wall more than a cannon, take advantage of those high defenses and use it's ability to make up for a lack in offensive, because one or two hits from foul play will bring it down if you don't.
One move that can give you a huge tactical advantage is power split, one of those highly underrated moves. Take a pokemon with almost no offense but massive defenses, power split with the toughest opponent. That opponent is weakened and your power swapper becomes invincible, possibly even a sweeper with the right damage moves.
There are also many moves you can use on an ally in doubles, like guard split for a highly defensive pokemon, use it on your glass cannon and that cannon becomes massive, while the user of guard split only suffers a little. This offers you a tactical advantage, which can win the match.
One other tactical advantage is the force switch, keep hitting your opponent with hard status effects in doubles matches and force them to switch their pokemon into attacks, with the right predictions you will easily win the match. Predicting your opponent's actions and builds is another way to claim the tactical advantage.
The most important tactic though, be prepared for anything. It is possible to build a team that is ready for any situation, in spite of claims to the contrary. Go through the moves and abilities of your teams, build a team that is capable of dealing with status and damage moves, plan on things like sleep, confusion, and poison. Expect the common ones, but do not forget the uncommon builds.
What brought this topic up was the fact that a lot of players who are cheating others out of rightful wins by disconnecting are either mega Kangaskhan players, or Smogonites. So I will take this last moment to add this, Smogon does NOT control Pokemon, if you cannot take the heat, change kitchens. Smogon has their own arena to battle in, those of us on Battle Spot are not interested in your rules, and most of us don't even know your rules, the few of us that even know you exist. So stop trying to force everyone to think like you do, in other words, stop cheating.