My closest friend is interested in polyglottery, what are the best resources?

My friend is very interested in getting into polyglottery. I guess a lot of language learners say that they want to be a polyglot, but she is really serious. I am an actual polyglot, so she’s coming to me for advice, but I got into it at a young age and have a natural talent for it; I don’t know how useful I can be. This is a problem that needs a solution. <br><br>Does anyone know of any resources that are geared towards polyglots in particular? I’ve never really come across anything that was specifically geared towards polyglots, only language learners in general.