Make sure that your sequence matches the source footage. For example, if your source footage is 1920x1080 and you place it on a sequence with any another setting, all exports, video and stills, will come out blurry. Make sure that field order is set correct as well.
That goes for exports as well, iow if everyting is correct and you export a 1920x1080 sequence as any other resolution setting you will see a quality hit. Provide more details for further help.