I. Find only higher quality videos when you do your searches. First, search for the key terms in a regular google search. Then, add this phrase to the end of the search query:
site:youtube.com “watch in normal quality watch in high quality”
II. Select the “watch in high res” option and copy the URL from the little URL box to the right of the video.
III. Get yourself over to Kepvid, enter the URL and pick the appropriate option to download or convert the video. Note that there will probably be an obnoxious advertizement that will try to trick you into clicking it to download the video. Don’t be fooled. Find the download link that is not inside the sponsored ad. If you want the high quality video, pick “mp4 – high quality” and save the file to your hard drive.
IV. Convert the video to any other format that works for you, depending on what you are doing to do with it.
V. Tweak the quality of the video when you decide to embed it somewhere else, by following these instructions.
See THIS for more info on steps I, II and III.