In the Adobe support section you can read an extensive tech doc about how to optimize the performance of your favourite image editing application.

Here is an executive version for your convenience:

1. Set a huge scratch disk
2. Fine tune File browser
3. Check if you need 16bit images
4. Adjust image cache
5. Deselect export clipboard
6. Minimize palette preview thumbnails
7. Make sure Async I/O plug-in is enabled
8. Disable Watermark plug-in
9. Optimize layers
10. Optimize resolution
11. Turn off maximize compatibility
12. Use Filter Gallery before applying filters
13. Drag and drop. Don't copy paste
14. Give more memory
15. Get a new Mac