Is there any microformat/standard for implementing search form on the site?
(access keys, naming etc.)
Any good practices?
The only things I can think of are that searches should be GET requests, and that you may want to implement a RESTful API that allows developers to query JSON and XML results in addition to HTML
If you are trying to implement a plugin for browsers like IE and Firefox to allow for search/autocomplete in the search box of the browser, check out this: https://developer.mozilla.org/en/creating_opensearch_plugins_for_firefox