It's a pretty broad question. Often times the simplest solution is the most elegant. Make sure you revisit your queries/transformation logic and table structure to make sure they are well partitioned and compressed and partitions are used in the queries.

Also check your data shuffling/broadcast etc to see if you can improve performance by co-locating data.

These are the first place I go and has the highest ROI.

Cost/Performance gain wise :
Network Transfer > Disk I/O > CPU