From the official Clash of Clans forums:
Building good defenses is just as important as aggressive attacking.
Upgrade your defenses, like Cannons, to improve your defense against intruders.
Upgrade your Army Camps to build a massive army!
Improve your army! Build the Laboratory and upgrade your troops.
Out of gold? Try upgrading your gold mines.
Complete Achievements to earn free Gems!
Clearing obstacles like rocks and trees sometimes rewards you with Gems.
Upgrade your walls to slow down the enemy.
Easily reorganize your village with the Village Edit Mode.
Defensive buildings like Cannons can’t shoot while they are being upgraded.
Gold Mines and Elixir Collectors do not generate resources while they are being upgraded.
Even if your village is completely destroyed, you always keep some of your Gold and Elixir.
Taking a break from Clash of Clans? Buy a Shield to protect your trophies!
Barbarians tend to attack the nearest thing, regardless of building type.
Archers attack anything in their range.
Goblins are greedy for Gold and Elixir. Their favorite targets are resource buildings.
Goblins deal double damage to resource buildings.
Giants prefer to attack defensive structures like Cannons.
Giants can take a lot of damage. Deploy them first to draw the defenders’ attention.
Wall Breakers blast holes into walls, opening a way to attack to enemy buildings.
Wall Breakers deal major damage to enemy walls, but blow up themselves in the process.
The Balloon is a flying unit, which means that Cannons and Mortars can’t target it.
Balloons primarily target enemy defenses like Cannons.
Wizards can dish out high damage, but can’t take much in return.
Healers can heal your ground units, but won’t attack enemies.
The Healer is a flying unit. Air Defenses and Archer Towers can shoot her down quickly.
The Dragon is a mighty flying unit that can attack both ground and air targets.
Is P.E.K.K.A a knight? A samurai? A robot? No one knows!
The armor on P.E.K.K.A. is so heavy that the Spring Trap does not work on her.
The Witch’s projectile attack may be weak, but her summoned skeletons can distract defenses relentlessly
The Witch is highly vulnerable when all of her skeletons have been destroyed
Cannons can only shoot at ground units.
Mortars deal splash damage to all ground units near the hit location.
Mortars can only shoot at ground targets.
Archer Towers can target both air and ground units.
Air Defense’s rockets only work against flying units.
The Wizard Tower deals damage against all units in the target area.
The Wizard Tower can target both ground and air units.
The Hidden Tesla tower is hidden from attackers until they come close enough.
The Hidden Tesla can attack both air and ground units.
X-Bow uses Elixir as ammo. Remember to reload it after enemy attacks!
You can set the X-Bow to attack both air and ground targets at a short range.
You can set the X-Bow to attack only ground targets at long range.
The Inferno Tower burns Dark Elixir to power its flame. Be sure to keep it fully loaded!
The Inferno Tower can deal devastating damage to units it stays focused on.
The Inferno Tower damage rate resets to the minimum each time it switches targets.
Traps are hidden from the attackers until they get close enough.
Traps and bombs need to be re-armed after they have been used.
Seeking Air Mines do not detect Minions.
Be sure to upgrade your traps to keep unwanted visitors off your lawn.
The Battle Log shows information about attacks against your village.
You can watch Battle Replays from the Battle Log!
Destroying an enemy’s Town Hall always gives you one star.
An active Shield protects you from multiplayer and Revenge attacks.
You get a free Shield if an attacker destroys your village.
You get a longer lasting shield if your village is destroyed completely.
If you attack another player while you have an active Shield, you will lose the Shield.
You can attack the Goblin Horde (play single player missions) without losing your active Shield.
Need a bit more gold for an upgrade? Take it from the Goblins in a single player mission!
Trophies that you win are deducted from your opponents’ trophies!
Earn more trophies to move up to a higher League level. Higher level Leagues give better Loot Bonuses!
Each League Season lasts for two weeks.
Want more loot? Join a League and get a Loot Bonus for every successful attack!
If you have enough trophies, attacking any village will automatically place you in a League.
If you lose too many trophies, you can get demoted to a lower League. Fight for those trophies!
Upgrade your Town Hall to unlock new buildings and new upgrade levels for your current buildings.
Rebuild the ruined Clan Castle to join forces with other players!
Use the Clan Castle to request reinforcements from your Clanmates!
Troops in the Clan Castle will defend your village.
Troops in the Camps are for attacking only – they won’t defend your village.
Clan Castle reinforcement troops can defend your village from an enemy attack, or you can deploy them when attacking.
Spells can have a huge effect on the outcome of the battle. Be sure to use them!
The Lightning Spell damages units and buildings in a small area.
The Healing Spell creates a ring of healing that heals your units while inside.
The Rage Spell creates a ring of rage that makes your units stronger and faster while inside.
The Jump Spell creates a ring which allows your units to jump over walls.
Upgrade the Jump Spell to give your units more time to jump over walls.
The Freeze Spell prevents buildings and ground troops from defending within its radius.
Upgrade the Freeze Spell to disable defenses for a longer time.
You can upgrade your spells and troops in the Laboratory to make them better and stronger!
The Damage statistic in unit and turret info is measured as Damage Per Second.
You can’t cancel upgrades in the Laboratory once they are started. Plan ahead!
Camps, Clan Castles and Storages remain functional while they are being upgraded.
You can end a battle and be victorious when you have won at least one star in it.
If you see an offensive message in the chat, tap it and choose “Report” to report the player.
Use chat reporting only when necessary – don’t get carried away!
Revenge attack is unavailable against players that you attacked first.
The battle ends when you have expended all your troops, clan reinforcements and damaging spells.
You can Boost the production rate of Gold Mines and Elixir Collectors with Gems once they are upgraded to level 5.
You can Boost the production rate of Spell Factory with Gems.
You can Boost the training speed of Barracks with Gems.
Dark Elixir storages can be built on town hall level 7, but the Dark Elixir drill is unlocked on town hall level 8.
You can start looting Dark Elixir as soon as you have built the storage for it.
You can use Dark Elixir to summon the mightiest Heroes in the realm!
Your Hero can attack enemy villages or guard yours against enemy attacks.
Heroes are immortal, but they can be injured and must be healed before they can fight again.
Heal your hero by letting him sleep or by using the Heal button.
The Barbarian King is the strongest of them all. His consumption of Dark Elixir has made him grow bigger than Giants.
The Archer Queen is an eagle-eyed warrior who wields a modified, miniature X-Bow.
Heroes have upgradable special abilities that unlock at level 5 and can be used while attacking.
Clan tournament and troop donation counts reset every two weeks.
Android: Never give out your Google credentials to anyone.
iOS: Never give out your Game Center password to anyone.
Android: Supercell employees will never ask you for your Google account’s password.
iOS: Supercell employees will never ask you for your Game Center password.
Android: Sign in using your Google+ account to safeguard your progress.
iOS: Sign in using your Game Center account to safeguard your progress.