Learn your own languages' grammar.
Then learn (in all tenses) the below verbs that are (usually) followed by infinitives
Can / am able Must/ to have to To want to
Then, 'to be' and 'to have' (to go with the above).
Vocabulary...including a boatload of infinitives.
i, indeed, had to learn english grammar in order to learn spanish. When they taught us french as kids in school, it was just an exercise in memorization and I had ZERO conception that the various verb tenses actually mapped onto something in english!
This book (English Grammar for Students of Spanish) was useful to me. I assume there's ones for other target languages as well
https://archive.org/details/englishgrammarfo0000spin_q0j9_05...