Always Check for Open Source First!
This is a lesson I've learned the hard way. Typically, when we engineers approach a problem, we are excited about the prospect of solving it. That is, we almost immediately begin imagining how the code might work, or what sort of algorithm we might use. This is a hard habit to break, but if we don't force ourselves to gain a bit of discipline, we will often end up wasting a lot of time solving problems that have already been solved (sometimes many times over!) by other people. It is a very disappointing feeling to spend days or weeks implementing a partial solution to a complex problem, only to discover too late that somebody already wrote a solution years ago that does far more than yours ever will. I've often had to ask myself "Why did I bother with this?"
The simple fact of the matter is that before you start laying down code, or even writing up a design, you should take 15 to 30 minutes and search the Internet for open source implementations of the functionality you need. You should try to get in the habit of doing this consistently, so that it becomes a normal part of your thought process. Some sites that you should always include in your search:
SourceForge
Google Code Search
Java.net (if it's a Java project)
freshmeat
In addition to those sites, you should do some basic Google searches for the functionality you need. You will probably end up being surprised at just how much useful stuff you find. Many projects, had they taken this approach from Day One, could probably have built themselves almost entirely out of existing open source components, shaving development time to a tiny sliver of what it had been, and therefore saving money and making time available for the addition of truly new features.
