I have an atypical answer to this question, which is how I practiced Spanish (with Radio in the car) years ago, along with News programming on TV. I am now fluent, and teach it. I am told that I speak better Spanish than native speakers (I am sure that is a hospitable exaggeration, so I’ll take it) probably for the same reason that many foreign students of the English language end up speaking better than some native speakers, due to careful study of grammar and good vocabulary and judicious use of expressions. But this question is about pronunciation. I found that Radio and TV/Video programming are a great source, but you have a question to ask yourself. Pronunciation is varied. What are your goals ? Do you want to work on a Mexican accent, Spanish (Iberian), Puerto Rican, Argentinian, Colombian, Chilean ? This will influence the Audio source material you choose.
Here is where Grammar comes in.
I have not found that rattling off entire sentences is helpful (for me), other than for “loosening” the tongue to the new language (good). When listening to “live” Audio, and “repeat”, decide what you will focus on, grammatically. This time, pick out only Subjects (proper names, improper nouns, entire subject clauses) of a sentence… identify just the subject, and practice those. Next time, identify the verb… the verb, its conjugation (past, present, future), and its moods (Indicative, Imperative, Subjunctive Present/Past)… what was that ? …the Conditional, interacted with Subjunctive… wow, how different from how we do it in English ! In other words, pronunciation with a “purpose”.
Pronunciation will become easier when you know why you are saying something that way. How a word is sounded may also depend on the entire sentence… Is a sentence a statement, a question, an opinion, where key words may be stressed differently… again, pronunciation with “intent”, so back to grammar.
You’ll know you are getting there when you start singing along some lines of a Mexican Ranchera or Banda music, or rapid lyrics from a fun / fast Puerto Rican Salsa, or contemporary music from Spain ! …and understand what you are singing. Then there is the pitfall… the lyrics of some songs you enjoy may lose their luster when you understand what you have been saying all this time ! or the innuendos.
Finally, there may be no such thing as perfect pronunciation. I am a native English speaker, but have accumulated enough other languages (> 8) that my English has developed a curious mix of accents that folks cannot quite place in my twang. Nothing wrong with your own sauce, as long as the goal, mutual intelligibility, is achieved.