Spec is almost good - move those points from cruelty to shield specialization.
Glyphs are okay too but you might want to try sunder or cleave until you start pushing harder content.
Yes, gem defense if (and only if) you need to, after that, you would be well-served by gemming for stam. If you want to worry about socket bonuses at all, just hit the ones that give at least a +9 stam or more. For your meta activation, use an expertise/stam gem.
Soft cap for expertise (pushes dodges off of the table) is 26 which is a pretty important target to strive for for threat while the hit cap is 264 (depending on raid makeup) and not nearly as crucial.
As for technique, try to keep your camera pulled back to be as aware of your environment as you can, keep track of your healers and always try to plan a step ahead of what's going on. Ciderhelm has produced a number of informative videos on introductory tanking topics that you would probably do well to watch.
Rotation has been discussed extensively on this forum and you should be able to find a lot of posts/flowcharts without me reiterating it.