This is Modding Skyrim: Scripter's Edition (MS SE).
It is a guidebook on scripting in Skyrim. It covers everything from variables to events to states and SKSE scripting. MS SE is not necessarily meant to be read all the way through, given its length. Instead, it has an index so you can skip to topics applicable to you, or you can read the entire thing if you’re interested.
It is intended for both new and old mod authors.
http://www.nexusmods.com/skyrim/mods/70883/?
Really good info and put together very well. Even if you don't think you need to read this, please check out 5.1 Best Practices. The most common inefficiencies I see in scripts are overusage of external functions (like Game.GetPlayer()) and lack of using loops and/or arrays. With just a little know-how, someone can convert a long list of same-type properties along with a long list of repetitive code on those properties to a property array and a short loop. I once did this for someone else's mod and shrunk a 200+ line menu script with no loops to around 45 lines.
Most of the scripts were done for quests so far. They were probably done by the user DigitalParanoid who has been inactive for quite a while. Cleaning them up will be great obviously. Can you make a short list of scripts you've found like this so we can confirm that they are mostly quest related scripts?