Referrals

Article on the imminent conversion of games to HTML/canvas (or svg!): jump
Great article on the mathematics of experience points (XP) as a progression mechanism in games: jump
Helpful tool to figure out a formula given a set of numbers (such as XP at each level up): jump
Super impressive chess program in just 1023 bytes!: jump

Clash of Clans Strategy Guide

Below are tips for Clash of Clans, serving as guidance from level 4 onward. First, focus on upgrading resource acquisition and storage. Note that upgrading the gold mine requires elixir while upgrading the elixir collector requires gold. Be aware that operations are halted during upgrade of the mine and collector, thus sometimes it is necessary to simply wait for resources to build up before proceeding.

After upgrading the Town Hall beyond the first level, build additional mines/collectors so only one is down during upgrade. Remove obstacles to find gems. Be careful with some of the interface elements as it is easy to accidentally spend hard-earned gems. Save every gem to eventually afford a third builder hut for 500 gems.

The first 19 levels is mostly about building a solid home-base with good resource collectors, seeking opponents with weak defenses, and collecting trophies. Difficulty might be found in the single-player "Fool's Gold" and "Immovable Object" challenges...these levels require some ingenuity or additional research at the laboratory.

Build a strong defense by creating a double-wall around cannons, archer towers, and resource storage. Mines can benefit from defense protection when placed just outside the wall within range of defense units. Check that opponents cannot deploy forces within the wall...when moving an object, watch for the highlighted areas on the ground to be certain there are no holes. Lay traps and bombs on the interior and reinforce the inner wall around the secure area. (see diagram above) The interior can serve for resource storage or for housing the town hall and eventually additional defenses like the wizard tower.

When attacking an opponent, if there are undefended buildings in the corner areas, deploy a troop to each building at the start of the battle rather than waiting for the collective to spend valuable time running to every corner near the end.

The gem box yields 25 gems and recurs every 8 days (on average).

Additional strategy...
General: jump
Attack: jump
Layouts: jump
Top 6: jump

Further reading:
http://clashofclans.wikia.com/
http://toucharcade.com/2013/09/30/clash-of-clans-guide-how-to-win-without-spending-real-money/

CoC shares mechanisms found in other games: building construction (like OGame), resource collection and management (like Edgeworld), multi-player combat (like Edgeworld), clearing obstacles (like DragonVale), re-arming defenses after use (like Edgeworld), and freemium play (like Dark District).

http://virtualeconomists.com/blogs/news/10823889-6-free-to-play-design-lessons-from-clash-of-clans-to-engage-players-and-increase-profits
http://www.gamasutra.com/view/news/185406/Clash_of_Clans_5_keys_to_success.php
http://en.wikipedia.org/wiki/Strategy_video_game

Also interesting are the copies of Clash of Clans: jump