I feel kinda lost since when I first became tank, I was told that I need alot of HP. Now that I have got it - I think I need to change some of it to avoidance since 3.3 is fastly on its way and I don't really know how to keep my HP and avoidance in balance.
So basically the question is - What should I change to boost my avoidance but aswel keep my HP pretty high so I could be ready for Icecrown?
Gem stamina you can really never go wrong with stam.
In this case, you can go wrong. Running blood with 15 expertise means you're getting 2.75% more parries and dodges than you need, which eats into your threat & dps potential. Only Rune Strike avoids that trap, and the glyph is helping ensure your threat is solid.
On a sidenote, Swordshattering is on Xanxus' Marrowstrike. Rune of the Stoneskin Gargoyle gives 3% avoidance (via defense converting to dodge, parry and miss chance) but also gives 2% more stamina. If you're going to stack stamina, I'd trade runes as well.
I would replace your current meta with an Austere Earthsiege Diamond, picking up 2% more armor. This will improve your armor but also your attack power slightly (via Bladed Armor). To activate this meta, you do need a red gem (or orange/purple), which gives you the option to shift some stamina gems to expertise/stamina. This ultimately improves your EH from the additional armor more than the slight loss in raw stamina lost. Napkin math says you lose ~110 hitpoints for 2% armor, bonus AP, & expertise.
The expertise to gloves enchant (15 expertise) is another enchant to review if threat isn't a concern. I do feel 40 stamina to bracers is superior to the expertise to bracers (15 also), but it's really debatable when you're not at the soft cap of 26 expertise skill.
The logic of shifting away from pure stamina is the improvements in your threat & DPS. This matters far more for Blood as the majority of attacks are physical and can be dodged/parried by mobs.
@JokerFMJ - Definitely the Triumph sigil. I see ~3% avoidance when it's up.