Add following info to your application configuration file to trace WF related info

<configuration>
<system.diagnostics>
<switches>
        <add name="System.Workflow LogToTraceListeners" value="1" />
        <add name="System.Workflow.Runtime" value="All" />
        <add name="System.Workflow.Runtime.Hosting" value="All" />
        <add name="System.Workflow.Runtime.Tracking" value="All" />
        <add name="System.Workflow.Activities" value="All" />
        <add name="System.Workflow.Activities.Rules" value="All" />
    </switches>

  <trace autoflush="true" indentsize="4">
    <listeners>
      <add name="customListener"
     type="System.Diagnostics.TextWriterTraceListener"
     initializeData="WFTrace.log" />
    </listeners>
  </trace>
</system.diagnostics>
</configuration>

Note:

We can control trace by using trace switches, so if you don't want trace all the info, you can trace only errors by using following trace switches

http://msdn.microsoft.com/en-us/library/system.diagnostics.sourcelevels.aspx

Reference:

http://msdn2.microsoft.com/en-us/library/aa663362.aspx