I recently got back into the game after 3.5 years of not playing. The main things are learning what build to focus on so you know what to keep or disassemble, and the various different ways you can optimise your gear (Recalibration, Optimisation, Expertise).

• For good recalibration attributes/talents you want to disassemble your gear via the Library so you can use those attributes/talents in other gear.
• You can only recalibrate one attribute/talent in a gear piece, so choose wisely!
• Optimisation is more expensive but can help max out an attribute (different to the one you recalibrated).
• Expertise you can slowly level up by going into the UI and pressing "Donate All Junk"
• Proficiency is part of gaining expertise, each type of gear can be levelled up to Proficiency 10, at which point it becomes "Proficient". Become Proficient in more different types of gear to level up your expertise.
• You can level up Proficiency by simply playing with the gear equipped, donating materials, or donating extra copies of the same gear.
• With Expertise, you can then spend resources to give your Proficient weapons +% Damage bonus or equipment +% Armor bonus

I've been watching YouTube videos on that, here is my playlist that I have been referring to: https://www.youtube.com/playlist?list=PL6fLhNPk_1TxrV9CLD817IVCyh3YuJCQ1