<Project InitialTargets="TestMain" ...>
  ...
  <Import Project="Sub.targets"/>
  ...
  <Target Name="TestMain">
    <Message Text="Hello from Main" />
  </Target>

<Project InitialTargets="TestSubInit" ...>
  ...
  <Target Name="TestSubInit">
    <Message Text="Hello from sub.targets" />
  </Target>

TestMain-Target:
    Hello from Main
TestSubInit-Target:
    Hello from sub.targets