[Gregordinary]

I particularly like the audio courses from Language Transfer. They create rules that help you transfer words from English into a destination language.

For example, words ending in ation in English, will end in ación in Spanish. Further, these words are also 'ar' verbs.

Conversation -> Conversación -> Conversar

I've found it quite helpful, especially in conjunction with Duolingo. At some point, I realized what I learned via Language Transfer was applying more as I progressed in Duolingo.

https://www.languagetransfer.org/complete-spanish