Always 'Quit' open apps you don't use,
never, NEVER have 2 sessions open at the same time,
and try using lighter applications when you can (VLC instead of iTunes for music, Skim instead of Preview for PDFs, Preview instead of Photos for images, etc)
I have to use a 2012 MBP with Yosemite from time to time and if I follow these rules it is definitely bearable.
Always 'Quit' open apps you don't use, never, NEVER have 2 sessions open at the same time, and try using lighter applications when you can (VLC instead of iTunes for music, Skim instead of Preview for PDFs, Preview instead of Photos for images, etc)
I have to use a 2012 MBP with Yosemite from time to time and if I follow these rules it is definitely bearable.