|Nail Polish in water|
Find a small glass and fill it with hot water,(only put the water high enough to cover the polish top) put your bottle of polish in the hot water upside down, wait a few minutes then try and open it. Sometimes if it's really bad you may need to add more hot water and wait a few more minutes.
Another good thing you can do is to try and remember is to always wipe off the top of your bottles with a tissue soaked with remover after each use.
If you have any helpful tips feel free to chime in and leave it below in the comment box.