A lot of problems I generally see with the lists that have been posted here or elsewhere, is generally a problem of army balance, so I thought I'd go over it in a Tactica. And, before you say it, no, I don't mean balance as in game balance.
What I'm talking about, is the ratios of various types of units in an army. And, to begin with, I'll list what these various types are, and their function in a list.
Magic Characters: These are one of the most versatile roles, depending on the lores available, but their general purpose is a combination of support and damage.
Support Characters: Notice I put support, rather than combat. This is because a combat character won't do very well in this edition, and must have another role to fulfill. As most players know, this is either a high-leadership general, or a battle-standard. Alternatively, characters can do well in certain death-star setups.
Anvils: These are your generic, hard-to-kill infantry blocks. Either with numbers, or a good armor save, or both, these are meant to survive. Oftentimes these can be good recipients of buffs, allowing them the offensive power to kill something, or enough added defensive power to outlast anything.
Hammers: On the flip-side, these are your hard-hitters. Generally, these are more fragile infantry blocks, but as many people can attest, this also can include buses of hard-to-kill cavalry, or certain infantry like Chaos Warriors. Noone would deny those are hammers.
Flankers/Warmachine Hunters: These are your fast, small, and generally ranged units, although this varies. This also includes smaller blocks of ranged infantry, where larger blocks would probably go into the anvil category. These are used to deal with pesky warmachines, grab flanks to secure a combat's victory, wear down units with shooting, or to run down fleeing units.
Now, on to the part people seem to have trouble with, the balance of all of these. Obviously the exact balance depends on army, but there are a few hard and fast rules you can go by.
The first of these, is that the majority of your army should be either Hammers or Anvils. This is where specific army strengths come into play. A Lizardmen player will field significantly more Anvils, as they lack good dedicated hammers, while a Dark Elf player will often field nothing but Hammers. As a fast rule though, around half to two thirds of your army should be made up of these.
Next, characters, and the more important ones, wizards, are first. Generally, you'll want one level 2 for up to 1000 points, and one level 4 for higher than that. If your army has specific tools to assist with power dice, you can add more, usually another level 2 at higher points games. Some examples of these are Power of Darkness for Dark Elves, and a number of +1 power dice dealies for other armies.
Now, for support characters. Generally, you'll want around a third of your army to be characters, giving or taking some, depending on how good your characters actually are, and the synergy with your list. And, frankly, these characters come after any wizards. Once you have a good amount of magic, think about putting these in.
The most important of the two archetypes is the BSB. Do *not* forget to put these guys in, if you have the points. The rerolls for leadership increase the resilience of your army by a good deal, and they're a good buy for every army.
As for building them, here's the problem. Almost every single one will be Hero level, and they're going to be fragile. You'll almost never want to put a magical banner on one of these, as that's a quick way to get killed, though certain armies have banners that are good enough, or characters that are good enough to get away with this. Regardless, pack them up with defensive items and you're gold.
As for your general, apart from usual character-building techniques, make sure you have a body-guard for them. Generals are often very good in a proper Hammer unit, though take care to make sure they're not so fragile the General is on his own the latter half of the battle!
Now, the one that usually gets overlooked, flankers and warmachine hunters. Rather than being a certain percentage of your list, I'll just say that you should probably have 1 or 2 of these per every thousand points, for a generalist list. Warmachines are a powerful force, especially in the new edition, and you'll always want some of these to mitigate this effect.
Anyways, I believe I've gone over everything. C&C welcome, if anyone gives particularly good ideas, I'll update the thread with them. Thanks for reading!