What's the best practices for developing a web service with a WSDL as a start point?
Your question is a little vaque, but developing web services with .net is quite easy.
Using visual studio, most of the things are generated for you. You can add methods as
[WebMethod]
public string hello(){
return "hello"
}
and luckily once you deploy it, the wsdl is generated for you.
If you are looking to download some entities from a wsdl, you can use the wsdl utility and invoke a wsdl to download the entity class.
Check out the WCF Developer Center on MSDN - it has tons of tutorials, article, screencasts that show you how to create a SOAP based web service, based on code or WSDL.
Use SvcUtil to generate your service interface and then develop a service against that. Here is an example.
I found this question helpful when I had the same question in the past.
http://stackoverflow.com/questions/548314/create-an-asp-net-web-service-from-a-wsdl-file
The problem I had was that I was given a WSDL. I needed to create web service methods based on the contract that the WSDL provided.