If you don’t yet have an SSD in your Mac, it’s time to upgrade!
By far the biggest speed boost on a Mac comes with upgrading the Hard Disk to an SSD. A faster processor (i7 etc) will improve the speed of some tasks, more RAM can avoid a slowdown, buta faster SSD improves the speed of everything. If you still have an old Hard Disk I can’t say how strongly I suggest upgrading.
a faster SSD improves the speed of everything
I received an email today from Amazon telling me that 240GB SSD drives are AU$42.19. I just checked the US store and you can get a 1TB Crucial MX500 drive for $94.99. These prices are ridiculously cheap.