Solidity primer
Writing smart contracts is a subset of full Dapp deployment. One can write a contract and let users interact and use that contract via a Ethereum node client (eg. Mist). You can use live.ether.camp/contracts online to watch ethereum blockchain Tx (transactions), addresses and invoke contracts. But the full potential of Dapps enables UX (user experience) and more functionalities. For example see https://www.augur.net/ and http://oraclize.it/
But before diving into Dapp development it is important to get a good grasp of smart contract writing. Solidity is a fully typed language (based on javascript and C##) to develop and compile smart contract code.
Read Solidity tutorials, do a simple "Hello World" greeter and compile your Solidity code in your sandbox. See tutorials: * http://solidity.readthedocs.io/en/latest/
Also, Eris Industries tutorials show some useful strategies for structuring complex contracts:
OBSERVE BEST PRACTICES AND UPDATES BEFORE DEPLOYING LIVE AND TEST , TEST and TEST.
By Community (ref: ConsenSys)
http://forum.ethereum.org/discussion/1317/reentrant-contracts
http://hackingdistributed.com/2016/06/16/scanning-live-ethereum-contracts-for-bugs/
http://hackingdistributed.com/2016/06/18/analysis-of-the-dao-exploit/
http://hackingdistributed.com/2016/06/22/smart-contract-escape-hatches/
http://martin.swende.se/blog/Devcon1-and-contract-security.html
http://publications.lib.chalmers.se/records/fulltext/234939/234939.pdf
http://vessenes.com/deconstructing-thedao-attack-a-brief-code-tour
http://vessenes.com/ethereum-griefing-wallets-send-w-throw-considered-harmful
http://vessenes.com/more-ethereum-attacks-race-to-empty-is-the-real-deal
https://blog.blockstack.org/simple-contracts-are-better-contracts-what-we-can-learn-from-the-dao-6293214bad3a
https://blog.slock.it/deja-vu-dao-smart-contracts-audit-results-d26bc088e32e
https://github.com/Bunjin/Rouleth/blob/master/Security.md
https://github.com/LeastAuthority/ethereum-analyses
https://medium.com/@ConsenSys/assert-guards-towards-automated-code-bounties-safe-smart-contract-coding-on-ethereum-8e74364b795c
https://medium.com/@coriacetic/in-bits-we-trust-4e464b418f0b
https://medium.com/@hrishiolickel/why-smart-contracts-fail-undiscovered-bugs-and-what-we-can-do-about-them-119aa2843007
https://medium.com/@peterborah/we-need-fault-tolerant-smart-contracts-ec1b56596dbc
https://pdaian.com/blog/chasing-the-dao-attackers-wake
http://www.comp.nus.edu.sg/~loiluu/papers/oyente.pdf