Video Title

As long as you need to get your message across. You shouldn't be adding unnecessary words, but you shouldn't leave out some keywords. For instance if you were making a Bicep curl video you could name it something along the lines of "5 Bicep Curl mistakes beginners make" The keywords there would be "Bicep Curls" "beginners" & "mistakes" you should try to put these keywords into your description, not as just words, but embedded into your video description. Also, be sure to put them in your tags as well, it helps SEO a lot.
Moved to the strategy / technique forum. :)

I agree with the above. - As long as it needs to be but definitely not too long. If for SEO, you should be targeting 1-2 keywords, no more.