Quick answer
Build the three-character team you are playing before putting resources into side projects. Choose Gear by the set threshold shown in the current panel. Save reforging for pieces that have earned a place in that team. Choose Karma for the role you want that character to perform.
What to upgrade first
Give your active trio enough attention to function together before you split Gear and Karma resources across characters you are not currently using. This keeps an early upgrade tied to a problem you can actually feel in play, such as a team member that is not ready for its current role.
That does not lock you into one permanent roster. It is a cautious starting point: establish a working team, then make later investments when you have a clear reason for them.
Choose a set threshold before chasing stats
Start with the set panel on the Gear you have equipped. Current release guides describe a three-piece core with a useful two-piece complement, but use that structure only when the panel for your available sets confirms those thresholds.
The goal is a coherent set decision for the role you are building, not a named set that every character must use. If the available pieces do not make the threshold useful for your team, keep the choice flexible.
Reforge after the item earns it
Treat reforging as later optimization. First make sure the active trio has usable Gear; then consider it for a piece you expect to keep because it fits the character's current role.
Temporary pieces and items that do not match the role you are playing are poor early candidates. Waiting gives you time to confirm whether the item still belongs in the team before committing more resources.
Choose Karma for the current role
Before investing, check whether a Karma option is broadly usable or tied to a specific character. Broadly usable options can be considered when they suit the job you need now, while character-specific options deserve a closer check against that character's current role.
Neither category is an automatic pick. Use the beginner guide to keep early resources focused, compare role ideas in team compositions, review the character roster, and check updates when version changes could affect your next decision.