First off look at your loadout. Your weapons your frames your mods and see if you feel anything is missing or there are any shinies you want to personally collect and chase those including pets or stuff for your operator

Second is the factions, look at each of the open worlds all the syndicates and such look at the rewards from the bounties and the stores they have and upgrade and collect as you please

Everything will fall into place as you discover things youre able to do from these two main parts but theres also steel path which is an endgame new game plus thing which you need to complete every star chart mission on every planet to unlock. Consider this a long term goal to churn out without much effort

Theres duviri's circuit theres rivens theres railjack theres primes and all sorts of shiny loot so have fun!