I've found that taking a deep breath and a step back from the turmoil of badly written code can help immensely.. quite a few instances where you can see places where code can be consolidated into a single reusable library..

With this in mind, trying to understand the basic intent of the code is really important to me.. I write down a small note describing what each section of code tries to do... this allows me to focus on reuse as well as consolidate several segments together..

Related to this: in addition to liberal comments, updating documentation or in some cases, writing some document that describes the structure and function of a code block is very helpful to any person maintaining the code.. you don't have to wonder "what was that guy thinking" or "why did he do *that* ?".. its all there in a document.. and also provides a cursory overview of what has been going on without jumping straight into the code (I'm a big fan of the saying that goes "the less time you spend planning, the more time you spend coding")...
Caveat: Docs that aren't updated are worse than useless, though...