If you're having problems with your complicaiton showing up, then check what you have set for the Data Source Class in Extension General settings within XCode. Don't be fooled by the dropdown and have the raw filename for your complciation class, it needs have the precursor $(PRODUCT_MODULE_NAME). for it to work.
so
$(PRODUCT_MODULE_NAME).ComplicationController
NOT
ComplicationController
I was fooled in that it was an option in XCode and didn't think anything of it, but this change worked.
Other tips if things still aren't working for you:
Toggle the install the app from the watch using the watch app on the iphone, this will cause the template code to be reapplied.
Clean the project before rebuilding & installing
Ensure you have implemented the correct complication template, some only appear on particular watch faces, and it's not always obvious which is which.
Remove the App from both the iphone and the watch and re-install
Reset content and settings on the watch simulator if you're still having problems