This guide is meant as a general step-by-step guide for capped chars or chars aiming at level cap. It doesnt contain lists of specific equip, just examples.
1. Determine endgame gear
This is most important, since it can be very expensive to have to swap the entire gear setup around just because you got one new item which goes into a slot where you had an item with totally different but necessary stats before.
a) Compile a list of must-have stats found on gear. This is mostly dependant on class and build, examples are given in 3.
b) Compile a list of useful stats which you might be interested in when you have your main stats slotted. Examples might be efficient metamagics or guard effects.
c) Try to find out must-have items for your class setup. This will be named items with unique stats not found on other items, for my pale master the examples are Torc of Raiyum and the Epic Robe of Night. Reserve slots for these items, you dont want to have to trash and remake an expensive greensteel or upgraded item because you messed up here. If youre not sure whats important here, ask experienced players or post in the forums.
d) Try to find items which cover two or more of your desired stats and incorporate them into your equip setup.
e) If necessary, slot items which have only one must-have stat. Chose the ones with the best extras.
f) Chose one or two (for casters) slots with the least desirable named gear options for your greensteel. Especially a GS HP item should be in a slot without any good gear options. SP items can be swapped out after buffing, so they can go into swap slots. Greensteel is expensive and flexible, and the choice of greensteel equip should be considered carefully.
2. Plan your placeholders
Most of the time you wont be able to use your perfect endgame gear right away, be it because youre still leveling, or because you still have to farm for some of the items (no torc yet on DQ completion #28 on my wiz). You will need placeholders that cover your needs but wont force you to swap your entire gear around each time you get a new item.
a) determine the most important stat on a missing item and try to duplicate it, if possible in the same slot (example: no epic helm of frost yet? grab a +6 cha helm from the auction house)
b) If the stat cant be replaced, just slot an useful item that you wont miss when you acquire the planned endgame item.
c) If you miss a stat which cant be replaced in the planned slot (missing epic envenomed cloak but need con somewhere), try to slot the stat into another unfinished slot. (missing envenomed cloak and a ToD ring, put +6 con into a ring slot)
3. Examples for desired stats on gear (not claiming to be complete)
a) general:
+6 or +7 stat items for con and your main stats
greater false life or superior false life
+4 or +5 resistance bonus to saves
Heavy Fortification
Immunity items (mainly deathblock and disease immunity)
30% striding
Feather Falling (at least as swap-in)
b) caster
greater spell focus in your main school
archmagi or at least wizardry 6
greater/major/superior lore
Superior potency 6 or something comparable
c) melee
Wide assortment of weapons (trash killers, banes, DR breakers)
Attack bonus
Seeker
Sneak Attack (if not tanking)
d) AC build
Protection
Natural Armor
Insight AC bonus
Dodge
I might be editing this in future, feel free to add questions, comments, and suggestions