Tips on learning Mandarin, Russian, and Arabic?

I do not have any background in foreign languages and currently only know English, but want to learn Arabic, Russian, and Chinese.

I have courses for each one (with the exception of Arabic).

Does anyone have any tips on learning languages faster or better? I have learning disabilities which make me learn things slower than the average person as well as ADHD, so any tips from people with these challenges who have overcome them to learn a language would be great!

Hope to hear from you guys and gals soon! :)

Dan