Just to consolidate some of the things I put in that other thread--
Key things to do when returning:
1) Check out the quest log, and Records of Eminence. It's a Tutorial/Achievement style rewards system that can help you ease into 99+ content.
2) Look into Trusts, which Records of Eminence will help guide you a bit on. These are storyline NPCs that can be used as party members when you're at less than 6 people.
3) Talk to people. This thread is a good start, but don't be afraid to send tells, make shouts, etc. Most of all, don't get discouraged if you don't get responses right away. Keep at it; people are out there looking to make contact, even if it doesn't seem like it.
4) Check any Home Points or Survival Guides you come across, since those act as teleporters worldwide.
In regards to gear and content, generally the progression would go along these lines:
Starting Point (just returned): Records of Eminence (sparks gear), lower end Unity NMs, Reforged Artifact/Relic/Empyrean armor (at least 109), Macrocosmic Orb BCs, easier difficulty Merit BCs, Wildskeeper Reives, regular Skirmish (not necessarily recommended) and probably Yorcia Alluvion Skirmish
Next Step (your gear nearing ilevel 119): 119-128ish level Unity NMs, Reforged AF/Relic/Empy armor 119, higher difficulties Merit BCs (Normal/Difficult), Delve, Alluvion Skirmish, Escha Zi'Tah/Sky Tier 1/2, Incursion (pre-level 130), maybe Vagary
Mid-point (full 119, good practice with mechanics and strategies): level 130 and up content like Sinister Reign, Vagary, Escha T3 and some HELM NMs, Reisenjima T1, Unity 135 NMs
High-end (great gear, more experience with complex enemies) Reisenjima T2/3, Escha Gods/AAs,
The Hardest Crap in the Game: level 145+ content like Super Kirin, Warder of Courage (super Absolute Virtue), HELM NMs in Reisenjima, fighting me in Ballista