Hi there. Here are the 2 modifications that make the biggest difference in my experience.
- Rip out the functionality related to automated A/B test suggestions. This can have a brutal impact on EE performance depending on the number of content items you have. If you don't need A/B testing there is an easy way to turn off all functionality. If you do need A/B testing enabled, it is a bit more complicated but possible.
- There is a KB issue related to the "My Items" button in the EE ribbon that can slow down load times. kb.sitecore.net/.../549951
But the best advice I can give you is to view the "Network tab" in a browser's dev tools to see which specific calls are delaying the EE load. You should be able to pick out a few specific calls that are the worst offenders and then start there.