This is dependency on database instance like singe node or multinode or RAC type installation.Based on the network processecing bytes of data.
increase the number of parallel session/threads configuration settings.
Rule #1 in performance testing: specify your goal, and actually stop when you reach it.
Many of us enjoy performance tuning, and in itself, that is never finished: there are always bits that can go faster. Therefor, without respecting Rule #1 the amount of time spent on performance work could be massive, with little practical benefit to show for it.
So, start with your goal. Make it practical, and don't look too far ahead. A year is good, 4 years isn't. Try to end up with something like 'ETL should fit within an X hour batch window, even when volumes increase by Y%. Or 'Our near-RT jobs should be quick enough for them to run every minute'.
As for the technical bits, that depends on your database, database versions, and the tools and skills you have access to. If on Oracle 11R2+, try and see if your organization has someone skilled enough to get auto DOP working properly as a first step.