#4: Set Your Preferences
In the Catalog Settings preferences (Lightroom > Catalog Settings), you can adjust the standard preview size that Lightroom builds from 1,024 pixels wide to 2,048 pixels wide. The setting you choose will depend on your monitor size. You can also adjust the Preview Quality (High, Medium, and Low).
By adjusting these toggle boxes, you can optimize Lightroom for your computer and monitor. I have Lightroom set to create standard sized previews that are 2,048 pixels wide for my Eizo ColorEdge CG243W display because it has a screen resolution of 1,920x1,200 pixels. I also set the Preview Quality to High so that I can see the best quality preview as I edit images. Because I have my preferences set to the higher settings, it slows Lightroom down just a little, but with 16GB of RAM in my Apple MacPro, it is a small difference and I prefer the higher quality previews. On my laptop, I set the previews to 1,440 pixels wide as that is the closest setting to match the width of my Apple MacBook Pro’s 13-inch monitor. And because my MacBook Pro has only 4GB of RAM, I set the Preview Quality to Medium instead of High, which massively speeds up Lightroom on my laptop.