To get corners clean and keep them you need to use the crevice tool on your vacuum cleaner. And forget about mops (they just move the dirt around, but don’t really pick it up) or any other tool for cleaning bare floors other that a sponge or rag and a bucket of sudsy water, and clean the floors on your hands and knees. Its the only way to really get into the corners, and I know that this advice is not what most people want to do, but its what gets the job done.
Also, having a regular cleaning schedule does wonders. Good old fashioned elbow grease is what will get the corners clean and keep them clean.
Eddie