If you are using SlSvcUtil.exe from Silverlight 4 SDK and you get a StackOverflowException, probably it is because of a known bug of the application.
The solution found in the article Workaround for StackOverflowException when using SlSvcUtil.exe is to add a C:\Program Files\Microsoft SDKs\Silverlight\v4.0\Tools\SlSvcUtil.exe.config file with the following content:
<assembly name="SlSvcUtil, Version=220.127.116.11, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" />
Sometimes, starting the debugging WCF services can be a rather long task (for example, compile and deploy SharePoint solutions), so the WCF Test Client Tool can be useful in speeding this operation.
You can find it in the local file WcfTestClient.exe.
More details in the article WCF Test Client (WcfTestClient.exe).
WCF is heavely based on configuration, so it isn't really easy to debug; logging can help developers in understanding what's happening: what calls are made, what exceptions are thrown, and so on.
To enable logging, you have to insert the following lines in the web.config file of the service application (often it's just your web-site):
<trace autoflush="true" />
Then you can open you *.svclog files with the Service Trace Viewer Tool, found in the local file SvcTraceViewer.exe
More details in the articles Service Trace Viewer Tool (SvcTraceViewer.exe) and Configuring Tracing.