I found these two ways to make my game run more smoothly. if you have any other tips to add feel free to post
#1: Editing D3Prefs
Find the .txt file called D3Prefs on your computer either by searching for it or locate it.
It is usually in My Documents.
in this folder find the line HardwareClass "x" where x is any number.
Change this number to a 1 and save the file again.
#2: Run Diablo from a USB
Run Diablo MPQ files from USB
This removes a lot of the startup lag some people are experiencing, the faster response time the USB has the better it runs.
I saved the post from battle.net in case it ever gets removed.