Psijic Order skill line has some a few extremely useful skills and passives that you should get your hands on no matter if you play a tank, healer, DPS, PvP or PvE.
Summerset, the new expansion for The Elder Scrolls Online apart from the new landmass introduces new crafting profession: jewellery crafting. This profession is a little bit harder to level up and use but is also very rewarding since being able to craft set accessory pieces unlocks a whole new level of depth when tinkering with sets for your character.
Elder Scrolls Online, just like any MMORPG game is suffering from the same "expansion fatigue" as any other. At first, everyone is hyped for new lands, new lore and new main story but when the dust settles it turns out there is not much left to do but to wait for the new expansion. Zenimax Online Studios addressed this issue before the launch, listing out items you can do besides the main story arc.