Welcome to Captain's mode. You suck. I don't care how many games of All Pick you have played, or how many pubs you've stomped with Ursa, Captains Mode is the style of the Gods! (or the pros or whatever) So, sit back and enjoy, this is my take on how to pick heros in a way that's effective and WON'T get you flamed at :)
Captains Mode is DotA. It's the only way to play a (as close to as you can get) balanced game. You will experience less n00bs in CM, primarily because people who queue for it want to play a game where the OP heroes are banned, and you can actually play with a team that has good composition (1 or 2 carries, 2 supports, an initiator, and so on).
In captains mode there are 4 phases, the first ban phase, first pick phase, 2nd ban phase, and of course 2nd pick phase. Typically, the first ban phase is to remove and OP (Overpowered) heroes from the pool, or to take out any tier 1 heroes that won't fit into your strategy.
Next is the first pick phase, here is when the tier 1 heroes are picked up, and usually they are supports and initiators.
The 2nd Ban phase is used to hit any potential combos your enemies may have and to ban carries if the other team hasn't gotten any yet.
The 2nd pick phase is usually where the teams grab their carry and fill whichever laning role their team is missing.
The bans and picks are:
There are some things you need to keep in mind whenever picking a team. I have ranked them in the order of most importance to least (In my opinion), but for a good team you should be able to fulfill all of these requirements: (Each will be talked about in more detail later)
1. Have a strategy (Pushing, Turtling, AOE (Teamfight))
2. Make sure your lanes are stable.
3. Have enough disables!!
4. Fulfill the team roles (1 carry, a semi carry or two, some supports, an initiator, etc.)
5. Pick higher tiered heroes (The heroes that are the strongest in the current meta-game)
6. Counter as many enemy heroes as possible!!
7. Make sure the others on your team can play the heroes you are picking for them.
There are several different ways of approaching a game of DotA. I won't list all of them because they're are plenty, but I will specifically mention the three most common ones:
Picking a hard carry and simply defending him and your towers while he farms. Pick carries like Anti-Mage, Juggernaut, Faceless Void, etc. Also, make sure you have at least 2 supports so that your carry can farm safely.
Sometimes doesn't even require a hard carry. Get 3 or 4 pushers/gankers and go for kills and tower kills extremely aggressively to gain an early advantage. Some of the best pushers are: Shadow Shaman, Leshrac, Death Prophet, Broodmother, Enigma, Natures Prophet, and Chaos Knight (He can carry as well as push, a great pickup for this strategy).
Here, you build a team that can absolutely demolish the other team in 5v5 clashes. Obviously, you will want heroes with Aoe's and disables. You will want 2 solid initiators usually, in case one of them fails or their blink dagger is on cooldown. Some of the best heroes for this are: Tidehunter, Enigma, Dark Seer, Invoker, Leshrac, Earth Shaker, Sand King, Jakiro, and Faceless Void.
When you are starting the first picking phase, you should pretty much know what strategy you are going for based on the bans. As a general rule, AOE teams are good against Turtlers which are good against Pushers, which are good against AOE teams. It makes a triangle. Its useful to figure out what the enemy is doing so you can counter it most effectively.
It is extremely important to make sure that your lanes are stable in Captain's Mode. There are several different ways of organizing them, but I will talk about the most common ones:
This is what you see almost exclusively in All Pick, in Captain's Mode, it is suicide and should (almost) never be done. The reason is, you are gaining no EXP advantage because your jungle is being wasted, you don't have a 2nd solo lane, AND you have no kill lane that will consistently either get early kills, push a tower, or shut down an enemy carry. AVOID AT ALL COSTS.
This is very common and usually is your safest bet.
It consists of a solo mid hero that can have rune control and will be able to contribute to the team because of a heavy EXP and gold advantage. (usually NOT a carry)
Second, it has a solo off-lane(Dire Bottom, Radiant Top) hero that has some sort of escape mechanism (Blink, Windrun), or very effective lane domination mechanic (Enigma's Eidelons, Dark Seer's Ion Shell). The purpose of this lane is to simply survive and gain as much EXP as possible, usually heroes that only need lvl's and not as much gold go here.
You may have noticed that there are only 4 laning heroes in this strategy, that is because you have 1 hero making use of your jungle. The junlge Hero's job is obviously to jungle as fast and effectively as possible, and to gank lanes where needed.
Next, you have the 2 heroes in the Safe Lane, this is usually a carry and a support. The support's job is to deny as many creeps as possible, and to stack and pull if needed. Stacking and pulling is where the creep camp closest to your lane is stacked, and then you use this stacked camp to pull your friendly creeps into the jungle, thus denying the enemies EXP and gold, and pulling you lane safely back to your tower. For info on stacking check this out: http://www.dota2wiki.com/wiki/Creep_Stacking. For pulling go here: http://www.dota2wiki.com/wiki/Jungling#Creep_Pulling.
Lastly, The carry should be getting as many last hits in his lane as possible. It is his job to hoard as much gold as possible so he can rush his much needed items. EXP isn't a factor for most carries, Gold is much more valuable which is why a carry needs to be babysat.
I won't describe it in as much depth because the only difference is that now, instead of a jungler, you have a trilane (either in your strong or weak lane, it depends) that is focused on completely dominating that lane. It should be stacked and pulled constantly by one of the supports, and should have almost every creep denied and last shot. A trilane should have a carry, at least one ranged hero with a stun, and another hero with a stun or slow. Your goal should be to:
#1 Get all Last Shots and Denies
#2 Kill the enemies in the lane fairly early
#3 Kill the tower
Of course there are other strategies but because this is a basics guide, I recommend the last two laning combos as being the most consistent.
These roles obviously vary depending on your strategy, but even so, a team must always have a carry. Maybe not an extremely hard carry, but even a Queen of Pain can carry you until around 35 minutes. The main thing is, make sure that you have at least one, and never have more than one hard carry. There is only so much available Gold for your team and you should have to split it too many different ways.
There should always be at least 2 supports. 1 should be the hard support that gets close to no gold and buys Observer Wards all game long, the other should simply help the hard support buying the courier, make it fly, and pick up items such as mechanism, or pipes.
Even if you aren't playing an AOE team, you should still get some kind of initiation so that you team isn't confused about when to go in. Really any kind of Aoe stun, or some kind of huge damage spell like scream of pain or epicenter will work.
Make sure that your first picks and bans are geared towards heroes that deserve them. Here is my list of some of the strongest heroes in the pool. Of course, the "best" heroes change ALL the time, depending on patches and meta. The best way to find out is to watch high skill games, and professional streams.
Countering your opponents picks is an integral part of Captain's Mode and can easily win or lose you the game. You should always try to ban your own heroes counters, and pickup the counters of your opponents. For instance, if you see a Nature's Prophet, you may want a tinker so he can TP defend with March and Boots of Travel against the extra-mobile Prophet. Things like this can make it a whole lot easier in-game to deal with certain heroes.
Some of the basic counters are:
Tinker, Sand King, Alchemist, Death Prophet, Leshrac. (anyone with a Cheap AOE and/or TP)
Slardar, Bounty Hunter, Batrider (vs lanaya)
Treant, Lanaya, Nyx Assasin, Puck
Lanaya, Venomancer, Beast Master, Broodmother
Naga, Enigma, Rubick, Disruptor, Nyx (new spiked carapace)
Spectre (illusions), Zues, Natures Prophet, Disruptor (Glimpse them back)
These are some very random and basic examples, you will learn the most by watching higher skilled games and paying attention while playing.
No one wants a captain that's a know it all. Yes, you should make the final picking decisions, but please be open to suggestions, and make sure that the people on your team can actually play the heroes you are picking. My advice would be to wait until all of your teammates have chosen their heroes before taking the last one.
Good Luck out there!