Best advice is to use Oracle ASM for Oracle database.
Put REDO in separate asm group on fast disks (SSD).
Other stuff (if using SAN) would be to use as much spindles needed for DATA and ARCH, as suggested, best is to measure the iops with iostat and determine the required physical disk count to achieve the desired response times/throughput.
For local disks things change a bit, depending on your setup, raid controller (if any) but the principle is the same.
Either add more spindles or 'fix' the code