Q: I'm using rasters, how can I optimize their performance?

A: If you are using reasonably small image files, a few megabytes, then a simple TIFF will work.
If you have larger images, then adding overviews using GDAL's gdaladdo will improve performance. Also using GeoServer's PyramidBuilder to build a pyramid out of the images will improve performance as well. You can read a tutorial on it here.

When you are creating a TIFF using GDAL and gdal_translate, always use the -co "TILES=yes"