Here are some tenents I follow for list building. Note that I used to aim more for optimization but now I find myself focusing more on the theme. I have always believed you can build an army that has both a great theme and is also powerful in a competive environment. I like to build lists that punish the meta.
As has been predicted by many 40k Internet pundits the game has switched over from MSU Mech to Infantry Horde... It's really true and this is causing some problems for some of the Internet 40k gurus. I see a lot of CSM lists that feature only zombies and cultists for their troop choices. Some people tell me you can't go wrong with over 100 T3 models in your army plus throw in two to three Heldrakes with their amazing bale flamers.
I am always constantly reminding myself not to hate on army lists I don't like and I'm very picky. I see some people drooling over Azrael joined to a huge blob of guardsmen. I just don't see these types of lists as very competitive to be honest and I think they can be abused. If you choose to drink the new koolaid then basically you are going to be locked into this style of play. I find it very boring but hey that's okay.
On the flip side what ever happened to Grey Knights... They just seem to be considered poison now. While I am very dedicated to my CSM I still like to play my Storm Crowe army and it just seems to keep getting stronger and stronger. Purifiers are still very much the death of hordes with their Cleansing Flame.
Typically what you see currently for most horde armies are two to three super blobs with one lead by a fearless character. They might be hiding behind an Aegis Defense Line for the 4++ and now you've got Azrael with his 4++ super bubble of iron. If you can pop these characters (e.g., Azrael, Juggernaught Lord, Typhus, etc.) early in the game the other big units can crumple... Live by the sword, die by the sword.
As much as some people say CSM is not competitve I see a definite pattern emerging... The zombies are really good mostly since they are very cheap and Fearless - so they don't need an attached character to lead them. There are also some very nasty combos such as Necrons and Orks. I tip my hat to anyone playing a pure army but that said I am very much a big fan of allied armies and double FOC.
I am really liking the new Ravenwing... A highly mobile elite army that can pour out lots and lots of fire power. I think I will eventually play this army but it's at least a year off according to my present schedule. I'd like to see what else will emerge this year from GW before I make that kind of investment. I see the plasma talons as very effective versus any enemy flyer so if you want to build this army don't worry about Heldrakes.. Ravenwing can handle them very well.
So that's all for now.