use the following search parameters to narrow your results:

reddit:{name}

find things posted in {name} only

author:{username}

return things submitted by {username} only

site:{domain}

get links to pages on {domain} only

url:{text}

search for {text} in url

selftext:{text}

search for {text} in self post contents

self:{yes|no}

include or exclude self posts

nsfw:{yes|no}

include or exclude nsfw results

e.g.reddit:pics site:imgur.com dog

see the search faq for details.