Hello! To dust OFF is a phrasal verb we use when we talk about something we are going to use that we haven't used in a long time. For example, I start a new job next week so I need to "dust off" my skills. I need to remember and practice my skills so I can perform well in my new job. I hope this is helpful :)

The literal meaning of 'dust off' is to remove the dust from something. We often use it as an idiom to indicate that you haven't done something for a long time. For example, you might say that you're going to dust off your running shoes to show that you're going to take up running again after a long period of being lazy. You can also it use idiomatically for something which can't literally gather dust, for example, your language skills.

Su.Ki. describes "dust off" very well. A few others have mentioned "dust up". I've only ever heard that expression to describe a small fight or quarrel.

We "dust" our collections, etc. in our homes to keep them looking fresh. Example: I need to dust in the family room this weekend. We also can say "pick yourself up, dust yourself off and get back out there" meaning when something negative happens, you have to get yourself together and keep going. There's an American country song called "Kick the Dust Up" https://www.youtube.com/watch?v=3aMK_q2leDU It's about how it's time to have some fun after working hard all week. If you want to improve your language skills, you would use "brush up". I need to brush up on my Spanish skills. Hope this helps! :)

"Dust UP something" is an expression which means to get ready to do something you have done in the past but have not done for some time. "I really must dust up my French as I am going to Paris next year" This would be the usual expression, and personally I would never use "Dust off something"