1. Restart and back up LR at least weekly, if not daily. Check Optimize catalogue at that time.
2. Update to the most recent version of Lightroom. Check for updates under Help Menu.
3. Keep your video driver up to date.
4. If excess spot removal or local corrections are needed, it is more efficient to perform this in Photoshop.  Keeping a large history panel for these corrections will also slow you down. Clear the history panel if not needed by clicking the X on the right of the History panel header.
5. The order of Develop operations will also increase performance. Best order is Spot healing first (which will improve accuracy also), then global non-detail corrections, then geometry corrections, local corrections and detail corrections such as noise reduction and sharpening last.
6. Avoid corrections that you don’t need.
7. Increase the Camera Raw cache in Edit> Preferences> File Handlings (Windows) or Lightroom >Preferences >File Handling (MAC OS). Start with 2-3 initially but can go up to 20 GB if needed.
8. Reduce the number of presents that you store in your Develop module under User Presets. Thumbnails are generated in the Navigator panel for each preset which can slow down performance. Deletes one you do not use or need. Best to store your presets with your Lightroom catalogue.  This info is in Preferences> Presets and check Store presets with this catalog. Hit Show Lightroom Presets folder to document the location of these presets as well as allow you to delete the ones you do not use.

I was having a serious slow down in processing using Lightroom, and making these adjustments did help. I hope they help you as well.