If there are documented best practices, I have not found them yet. However, here are a few guidelines I use when determining where to put parameters in an url:
Optional parameters tend to be easier to put in the query string.
If you want to return a 404 error when the parameter value does not correspond to an existing resource then I would tend towards a path segment parameter. e.g. /customer/232 where 232 is not a valid customer id.
If however you want to return an empty list then when the parameter is not found then I suggest using query string parameters. e.g. /contacts?name=dave
If a parameter affects an entire subtree of your URI space then use a path segment. e.g. a language parameter /en/document/foo.txt versus /document/foo.txt?language=en
I prefer unique identifiers to be in a path segment rather than a query parameter.
The official rules for URIs are found in this RFC spec here. There is also another very useful RFC spec here that defines rules for parameterizing URIs.