There should be some guides on this site for DK tanking for the right rotations to produce the most threat. You definitely need to work on your gear though. Run some regular level 80 dungeons and get the gear you need from there first. You're defense capped already though, that's always good. You need a bit more health and armor though. After you run the regular level 80 dungeons (culling of stratholme, halls of lightning, utgarde pinnacle, oculus) and you have the tank drops from there, start doing some heroics and get some gear.
Your defense capped at the moment, but you'll need more stamina, alot more, you'll want at least 20k hp to start heroics, but everyone you group with will be happy if you have a few k more, replace all dps items (your two trinkets, they will be the largest +stamina boosters) And I'd advise swapping enchanting for jewelcrafting, you'll get some epicly nice gems and tanking trinkets with even more sockets for even more stats.
as for your spec, if you've been doing nothing but dpsing up to 80 as a DK and want to see what tanking is like, always tank in the tree you are comfortable with dpsing first to get the feel for it, personally I like to see things as I'm a crazed dpser who doesn't care about aggro ^^.
back to the spec >.>
Okay why is it most people I see have howling blast, but not the glyph? >.>
Get Howling Blast glyph. trade runic power mastery for imp icy talons, you don't 'need' chill of the grave either. put points into bladed armor/dark conviction. These changes will give you a Good Solid build for every heroic and ten man (my spec, my experience). Like I said though, go with the tree your comfy with.
and glyphs your looking at obliterate, HB, (frost strike most likely, HB glyph replaces need to cast icy talons) and raise dead/blood pact for minors.
If your happy with frost and you've made these changes, use the macro for rune strike on HB/FS/OB. then go dps some stuff and see how it all works for you.