I’d like to start an opensource project.
Pick the social contract. I’ve learned the distinction between open source products and open source products. The latter is a social group of people collaborating to create an application. The former is an application that the developer will give the source code for, but doesn’t necessarily do collaborative development outside of processing bug reports, etc.
Pick a host Codeplex is a good host for MS centric projects. Sourceforge is good because it is big. Google code is also not bad.
Check your employment contract and pick a license I can’t help you with the first. As for picking a license, pick something that protects you from lawsuits and is compatible with other open source licenses. Licensing is partly governance, so put some thought into how you plan to govern your application and your relationship with users and other developers.
Pick tools that are widely available. If you can only open the source code with an expensive proprietary IDE, you won’t find many friends to help you. In the .NET world, the ideal project would be able to compile in Visual Studio Express and MonoDevelop.
Pick compatible libraries. Closed source applications have an easier time here. If you are completely ripping off someone’s libraries in an intranet application, the rights holders might never discover. In an open source application, it will eventually get indexed and lawyers will look over your code looking for lawsuit opportunities.
Don’t make it hard to install You may love SQL Server. But taking a dependency on something as user friendly as SQL Server will decimate your potential user base. In the case of SQL Server, either choose SQL Compact or Sqlite. MySql has the the problems as SQL–it is a bit to hard for people to use. Your app will not likely have a DBA– even if a company picks up your product, it will likely be a small company that still doesn’t have a DBA. It should work by unzipping into a directory and be portable on a thumb drive.
Ask for help Ask for help in your app– set up something like a uservoice page for feature requests and discussion, a bug tracker that accepts public input.