Psychic powers & defense! I said it when I picked up the 5th edition book and I’ve said it every time a new army comes out, psychic is back (maybe not as ridiculous as 2nd ed) and you need to deal with this. For most armies this is pretty simple (Eldar, Tyranids and Imperial armies) where you have some sort of psychic defense. The other armies? Well only really two are competitive (DE and Tau) due to their awesome gun array. Since Eldar are running a Farseer anyways we don’t need to look at what they need to take for psy defense and Tyranid psy defense is incorporated into their army as well up close. However, taking a Deathleaper will improve your psychic defense quite dramatically even when outside of Shadow in the Warp so it’s a recommended Elites slot. For Space Marine armies you’ve got a lot of options in Libbys (& Dread Libbys), Rune Priests, GKTs w/Hood and Inq w/Hood whilst other Imperial armies carry theirs around with them (GKT and SoB) or need to take Inq/GKT w/Hood. Either way, you should be incorporating a Hood/Staff into your army otherwise certain spells well be your undoing. Consider psy defenses to be an extra 4+ save to prevent damage. We all like cover, yes? Take your cover with you.
And the other concept I needed to lay down was something GWvsJohn called forced choices. This is where you give a gun in an opponent’s army multiple targets. This is most often done with saturation (i.e. autocannons like to shoot at AV10-11 but if you have 10 AV10-11 you’re going to overload those autocannons). The idea here is if you have so many ideal places for your opponent to land shots, they aren’t going to be able to deal with them all. Furthermore, if they have to make a choice they are more likely to make a mistake. The opposite of this (and generally bad option) is giving a target to every gun from the beginning. This generally happens with bad hybrid builds (i.e. no bubble-wraps, JSJ troops, etc.) as all those anti-infantry guns and anti-tank guns get a target on T1. More damage = less army.
So how do we incorporate this into our army? Certain guns like to shoot at certain things. Most blasts like to shoot at infantry, higher strength weapons prefer shooting at higher AV (this will also be covered later in target priority), medium strength and good rate of fire weapons like to shoot lower AVs, etc. To make a forced choice outside of saturation you need very specific units for this. A really good example is Tyranids. Raveners and Warrior variants are T4/W3 and subject to ID. This means those S8 guns are perfect for shooting at these units but they are also perfect at shooting at MCs. These are two completely different units and thus force a different choice that target saturation does, do I take out the Warriors or wounds off the MC? By forcing your opponent to make such choices, they are likely to make mistakes.
This is the advantage of pure armies (i.e. foot or mech) over hybrid. Whilst certain hybrid builds wreck havoc (i.e IG & Tau), others (i.e. BA, SM, CSM, etc.) can be good but not as competitive because against a balanced opponent their T1 fire is going to be more effective than yours. An all foot list laughs at all of those S8+ guns heading their way (as long as they are an effective foot list) whilst an all mech list early laughs at the anti-infantry fire. These brief moments of ‘security’ give them a leg up on the competition.
So by incorporating psychic defense your army can better stop other psychic powers (both offensive and defensive) which gives you more control over what takes place on the board whilst forcing your opponent to make choices makes the game harder for them and increases the chances of them making a mistake. Sorry these weren’t included in the first post, it was a bit long anyways! Will do target priority next.