After rolling my warrior tank after playing pally tank for many years I would still advocate 3 things particually when tanking
1. Wherever safe and possible tank with the mob between you and healer/dps pack. This usually involves a little positioning at start but can be a life saver. First and foremost nothing ever runs behind you everything is forward and you can see and use all your attacks. If you taunt is on CD you can charge a lose add and mocking blow it or shockwave it and then shield slam. My usual manouvere whenever possible is charge in at mob thunderclap, shockwave move past them while stunned turn and start tab shield slamming etc. There are alot of adds with forward only attacks as well and you will find things like forked lightning etc are minimized by turning mobs. The danger in this approach is pats etc coming up behind you but at the end of the day thats all about knowing the mobs in the raid. Certain bosses you can't do this for because it puts the healer to far away but those instances are minimal.
2. Being a tank is an undertaking and it's expensive. You do not go in under def capped, under chanted and gemmed and under consummable prepared. Same is true for healers because for both these roles not doing your job the raid wipes. DPS is the easy role in this game you can go in unprepared uncapped and get away with it just may take longer to kill and hey we can blame the tank/healer if we fail. Tanks also face the biggest repair bills in the game so tanking and being cheap arse isn't going to work.
3. You need thick skin and a sense of humour as tank. The fact is you are going to make mistakes and wipe, other people are going to make bad's and wipe and you may still get the blame (DPS never own up to mistakes). If you can't live with that then start collecting dps gear NOW and respec.
** Remember Warcraft players fail in directions you never thought possible.