This will certainly become an eclectic list, but here's a list of patterns/moves/ideas that can be applied to various situations. (And yes, that sounds as abstract as I want it to be.)

  1. When storing many pieces of data, and this data may be appended to, store them as separate files in a directory rather than putting them all in the same file. This storage format is suddenly safe to be concurrently accessed; readers and writers don't block each other. (Similarly, make each separate file immutable.)