Almar's guide is good, but I'm going to write the abreviated version I wish I'd had after upgrading to Heroic toons.
Three things to consider: What class-type? All-Access? How fast are you leveling?
Tanks should really be All-Access so they can augment for AC (prestige) and get the tanking AA's via auto-grant. Melee get decent atk/stats/weapons from prestige gear, but it's not make-or-break. Casters/healers can do fine in weaker gear, maybe grab the armor slot for nukes/heals or an Enhanced Minion ear if you need a pet tank. Sometimes I'll gear my puller up right after the tank, but that's more for lag surprises than a requirement.
Follow
Maskoi's rules for multi-boxing: For your tank, upgrade often and focus on max AC. Next upgrade your group DPS so you can kill faster and give named a shorter window to spike your tank down. Finally use the trifecta in your group (tank/healer/cc) if available.
When I'm grinding toons up, I upgrade every 5 levels or so, since I know I'll wear the gear for awhile. If I'm powerleveling, I skip many levels of gear including taking toons to EoK/RoS with some empty gear slots. The 95 Fear Touched set or 100 Castaway are decent hp jumps, so I'd recommend one of those if nothing else.
Tradable & non-prestige armor sets, the pieces are random drops from named in these expansions, sometimes quest/chest rewards and sometimes available for instance tokens:
85 - HoT armor, HoT T1 not tradable and similar to your 900 hp heroic gear. Take it if exp'n there, otherwise skip it. T2/3 are 1000+ hp.
90 - Rustic armor (VoA T1) = 1400 hp gear
95 - Fear-touched armor (RoF T1) = 2200 hp gear (results are called Boreal armor)
100 - Latent Ether armor (CotF T1) = 2600 hp gear
100 - Castaway armor (TDS T1) = 2800 hp gear
105 - Glowing Seb armor (HH Old Seb - zone closed for 2017, Bazaar?) = 4200 hp gear
106 - Conflagrant armor/gear (RoS player made) = 4600 hp gear
If you're going prestige there are tier upgrades to some sets. Like Castaway has no-trade/prestige Tideworn & Highwater sets above it.
If you're full Free-to-play (no TBM/EoK) then the armor and weapons from TDS are tops until next expansion opens TBM for you. Castaway (100/tradable) drops from named in the first couple zones or the first TDS vendor, most of the Tideworn set is on Brother Island. Do not AFK bot on Brother Island. It's too small and too popular. To get the rest you'd need to work on your TDS zone flags to open more zones.
At 101 you'll want to start buying your TDS class type-3 spell/skill augs from the vendor in Katta Deluge (TDS)
If you have TBM:
75-105 - TBM Vendors. Bazaar shop or farm "remnants of tranquility" for TBM gear, augs & weapons. This set is interesting in that you can keep buying aug upgrades as you level to improve the whole piece. Remnants are rewards for finishing the various missions in TBM, they're tradable and re-covertable to trade items from your alt-currency tab. The 105 versions are a step below EoK T1 drops, so not too bad. Some vendors require faction, but you can build a full armor/weapon set without those vendors.
At TBM they add type 5 augs (+ heroic stats) and those continue to EoK, so it's easiest to buy your TBM vendor type 5's and just use them until you buy/find upgrades. The EoK upgrades to type 5 augs aren't that major.
105 TBM Vendor armor & vendor augs = 2700-3300 hp gear. Wide variety of options on aug'n it, so hp varies.
If you have EoK:
105 - Buy invis potions if needed. Head to Frontier Mountains. If you can kill the named, get to it. Otherwise learn your camp names and hang out/exp near Bi`f camp. Wait for rot calls in /ooc or /general, Bi'f will be the most common spot. You can get most of your T1 armor set in a week or so just from rot calls. Lcea works too, but will be a bit slower. Gear up until you can drop named, then finish out your remaining slots/augs. If All-Access you can head to EoK T2 zones for prestige upgrades.
105 - EoK T1 no-trade armor = 3900 hp gear
105 - EoK T2 no-trade, prestige armor = 4100 hp gear
If you have RoS:
105 - Head to The Overthere. You can buy your 106-110 spells/skills here and pick up your new type 3 augs. People are still gearing themselves and alts, but you will see some rot calls from time to time. Some of the named are boxable. OT and Skyfire named drop some non-prestige weapons & non-vis armor. If you are prestige you can also continue farming through the T2 zones.
The RoS armor sets are a continuation of the EoK T2 set, so you'll need to have the EoK T2 pieces to upgrade them to RoS T1 or T2.
If nothing else you can farm conflagrant ingredients to sell/trade up for conflagrant armor/weapons. If you get a chance, start working on your VP key in OT as that flagged RoS zone has the best groupable drops.
105 - RoS T1 no-trade armor (aka EoK T3)= 4400 hp gear
106 - RoS T2 no-trade, prestige armor (aka EoK T4) = 4750 hp gear
Non-vis slots and weapons tend to be every 5 levels, but there are a bunch available at level 92 specifically. So I'd Bazaar shop deals at 90/92/95/100/105 and then figure out where you need to go for the missing items. If you are named farming, that is straight forward. Otherwise fill those slots from
ETWK vendors via CotF Heroic missions(75-100 with some lvl 100 gear being non-prestige),
TDS Vendors (100-104 with Tempest Thule vendor selling non-prestige) or
TBM vendors (75-105 with nearly all non-prestige.) Conflagrant weapons/gear become available at 106.
Augments will be nearly all prestige, but each expansion has quite a few. The AC ones can be competitive camps even a few expansions back. One benefit of going Heroic, is you can do Heroic Aug quests starting in Feerroot the Dream. They are a quick way to fill those slots and are non-prestige.
AA & Auto-grant: A Heroic toon gets 4k to 5k AA at level 85. If you have All-Access and turn on Auto-Grant AA, you'll gain free AA every level and wind up around 9-11k AA by level 100. A common strategy is to wait until 100, then go All-Access/Krono + Auto-Grant to gain all granted AA, then try to grind as much as possible while you have All-Access for a month. Auto-grant was a bit confusing, but what it does is give you every available AA that your level could earn, excluding AA from most recent 4 expansions. So currently it doesn't grant any AA beyond level 100.
Where the heck are my next spells/tomes:
1-90 - Plane of Knowledge Library
86-90 - Rank II are from Nebulous Dream Fragments.
91-95 - Argath (VoA) Note there is a special spell vendor for pets/auras. (Alaran Cantrips for Rank II)
96-100 - Shard's Landing (RoF) (Rank II for Dreadmotes)
96-100 - ETWK (CotF new spells) (Rank II on vendors for Marks of Valor)
101-105 - Katta Deluge (TDS, most of your spells) (Rank II for Briny Essences)
101-105 - Plane of Tranquility (TBM new spells) (Rank II for Essences of Life)
101-105 - Lcea (EoK new spells) (Rank II for Writs of the Combine)
106-110 - The Overthere (RoS) (Rank II for Clawed Tablet of the Ring of Scale)
For ports, they're often in the port-to zone but on a separate vendor. Try "find."
J5 Mercenary Quest: If you're using mercs, you might as well unlock the best available which is the Journeyman 5. Heroic toons get a fairly easy
15 minute quest in Feeroot the Dream. Alternatively there is the original
"Rathe" flag in SoD progression for J5 access.
Further reading:
Get to the Beach (Great out of the way leveling spot.)
EQResource - Has the best general reviews of named/gear for each expansion.