In my experience, most Pokémon battles are lost because of one of these three things:
1. Your team, while made up of good Pokémon, only works as isolated powerhouses, not as a functioning unit.
2. Your team works so well with each other that your strategy was apparent, and someone exploited its weaknesses.
3. You just lost. Bulbasaur happens. Try again.
What if I told you I have a solution for problems one and two? I know you are curious. The answer to all your questions are just a click away. As long as all of your questions pertain to this specific subject.
We've all seen it happen. A "perfect" weather-based team, baton pass team, or any other scheme-like team get foiled by a simple exploitation of one of your weaknesses*. In this sense I don't mean type weakness, but strategy weakness. A weather team fails if the skies change, a baton pass team loses if a link in the chain is broken.
On the other hand, you don't want a team of Pokémon that can't even work together. It's called a "team" for a reason. There has to be some cohesion or you are just left with a greatest hits collection that doesn't have any identity.
But what if you could have a strategy that is so subtle your opponent won't even notice, even after you've won the match? I'm going to call it "Subtle Team Synergy" and I'm going to give you two examples you can try out.
Chapter 1: The Bait and Switch, Or: "If You Strike Me Down I Shall Become More Powerful Than You Can Imagine."
A good strategy is one you already have set up before your opponent knows what you are going for. The first strategy definitely fits this category. I'm sure that there is another name for it, but "The Bait and Switch" works fine. This is where you anticipate an attack of a certain type, let's use Electric for an example, than switch to something that becomes stronger when hit with that type of move.
Continuing with our Electric example, you would put up something that fatally weak to Electric, Gyarados would work in this instance, against a Pokémon that you think would use an Electric move on it. Then, quickly switch over to your Electivire, who gets a boost from Motor Drive and is now faster than anything it will come up against, and with a wide array of types to choose from in its move arsenal, is set up to sweep.
A key element to this strategy is not letting your opponent see your whole hand. Don't bring out that Electivire until it can get the boost, because you are just giving your opponent more information to predict your gambit.
Alternate Pokémon that can use this strategy: Pokémon with the ability "Justified," "Motor Drive," "Lightning Rod," "Storm Drain," "Sap Sipper," or similar abilities.
Chapter 2: The Moxie Sweep, Or: "Can't Stop The Rock, Can't Stop The Rock."
I know this one works, because I use it to great effect all of the time on Pokémon Online. (I play in the Dream World tier.)There are a few different ways to run this, but I do it with my Heracross, who has the following set-up:
Heracross w/ Choice Scarf
EVs: 252 in Attack, 252 in Speed, 4 in HP
My team is basically set up to take out whatever threats could take out Heracross before I bring him out. Many of Heracross' threats are typical leads, namely Ninetales, and fast flying types like Aerodactyl or Zapdos. I take out anything that could give Heracross a little trouble, and wait for one of my Pokes to die before I switch to Heracross. I don't switch into Heracross outright because his defenses aren't enough to take the first hit, so I wait for one Pokémon to die to give Heracross an open shot. The Choice Scarf is to ensure that he always goes first and never has to be hit.
I have Heracross set up to OHKO as much as possible, hence all of the differently typed moves with high attack power. Once I take out one Pokémon, which is easy to do as long as I get a super-effective, Heracross gets an attack boost and is able to OHKO most things that don't resist him. After two KO's he can even take out Pokémon that resist the move type.
That's about it, you sweep after that's all done. Just a warning, if you've seen a Pokémon that is immune to one of your Moxie Pokémon's attack don't lock yourself into it with Choice Scarf. It would be a shame if you set up a sweep perfectly and then end up using Close Combat on a Gengar.
Alternate Pokémon that can use this strategy: Anything with moxie. Easy.
There you have it. These strategies aren't too crazy, but they are also hard to spot when you are facing it. I hope they work for you!