How can you mark some tests to run only those? From all the test that you have in different folder to mark some as sanity and only run those?
If you are using SpecFlow look at the Tags Tags description where placing a specific tag before your Scenario allows you to run the specific ones you want. I use @test or @dev for specific User/Functional Tests and when using my NUnit Driver I put in the tag with the /include option. This links in to the SpecFlow feature files such that the following case will check that I can get to the Home Page when I use the @test tag.
@test Scenario: Access the Home Page with Internet Explorer Given I have started Internet Explorer When I go to Web Site Then I should see the home page
They are very powerful and very useful in structuring your tests.