In The System tab of User Preferences goto Opensubdiv Compute and try using OpenMP or CPU.
Also on that same tab, scroll to the bottom and increase your Memory Cache limit. It should be set to 1024 by default. If you have 8gb of ram, then click that box and type *7 after the number 1024 (so 1024*7) which equals 7168, which means that blender will use 7 of the 8gb of RAM for memory. Be careful and play around with this value, try to stay in multiples of 1 so you use 1, 2, 3, 4 ect GB of RAM.
To better fine tune blender to your machine, read up on the settings available to you in the user manual.
I would suggest working in blender internal, as this side of blender is not so resource intensive. You may also want to work on low poly projects. This will also help you with modeling.
However, if you would like to speed up renders in cycles, take a look at this video: 18 Ways to Speed Up Blender Cycles Rendering - https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwiGiNO38abbAhVhITQIHcloBGAQFggxMAE&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D8gSyEpt4-60&usg=AOvVaw2jR9KDsJDWUto-lZ-N4csG
You could also optimize your windows start up by removing things that you don't need to start when your computer boots up. De-fragment, and uninstall any programs that you don't use anymore. Aside from that, I do not believe there is much you can do without upgrading your hardware.
You can also render files without blender open, to my understanding, from the command line. There are several tutorials on youtube about this. And even addons to use for this purpose.