Pimsleur has been the core of my instruction in Brazilian Portuguese, and it's been a wonderfully effective program. I like it because I can listen to it in the car, at the gym, or at home, and I don't have to be sitting in front of a computer. I have found the spaced repetition to be a good match for my learning style.
However, I do not use the program exactly as described in the audio guide that accompanies it. I know that the guide will tell you that you can move on to the next lesson if you know about 80% of the material covered in a lesson, and this is probably true, but I prefer to repeat a lesson until I have reached a higher level of competence. This is a personal decision, and for some learners, the motivation of moving through the program at a faster rate will outweigh any benefits to repeating a lesson.
Pimsleur actively discourages students from writing as they listen, and I agree with this when you are first hearing a lesson. However, there is no reason why you cannot go back to a lesson after you have learned the material and use it as to develop writing skills, too. This will not defeat the audio-only approach of the program, as long as you do not attempt to write during your first exposure to the material.
The following suggestions are some strategies which I have found to be helpful in getting the most out of this program.
1. Listen the first time just to listen. Really pay attention to what is being said, try to visualize the words if you can, and if there's any word or phrase that really has you stumped, replay it until you have a good idea of what is being said. I often do this first listening at the gym, where I obviously do not attempt to repeat the lines out loud.
2. The second time through, repeat everything out loud, and again, go back and replay any phrases or sentences that are very difficult to say. Yes, Pimsleur will cycle back and have you say the same thing in upcoming lessons, but the faster you can get an accurate pronunciation, the better.
3. The third time through, go for mastery. At this point, I am usually able to repeat about 90% of everything in the lesson with fluency and almost automatically. The automaticity becomes even better as you hear the same phrases and sentences repeated in succeeding lessons.
4. Use the opening dialogues as dictation, but only attempt this after you have progressed about 5 lessons ahead of the lesson that you're attempting to transcribe. Why? The dialogues often include vocabulary that is not actively practiced in the lesson in which the dialogue appears. It may not come up for another couple of lessons. Going back to the dialogue after you've moved beyond the lesson gives you a review, and increases the likelihood that you'll be able to write down what is being said.
5. Write a script for the rest of the lesson. "Script" may not be the best term; you can write phrases or isolated vocabulary words, but it really does help to have something written down. Do not attempt this as part of your listening and speaking practice, though. First of all, it's going to slow you down too much, and secondly, it interferes with the whole Pimsleur approach. However, once you have mastered a lesson, there is no interference in learning if you go back to it and write down what is being said.
6. A word-by-word script is probably excessive, as the same phrases are repeated in different sentences, but a list of isolated vocabulary words is probably not of much value. I have found that by writing key sentences and all of the new vocabulary in phrases (they will mean more in context than in isolation), it provides me with a written review that I can read aloud without the lessons actually playing. This gives added reading and pronunciation practice, helps me to focus on grammar, and reinforces vocabulary that doesn't appear as often in the audio lessons (Pimsleur definitely repeats some words more than others).
7. Use what you have learned, even if it means that you talk to yourself. I don't care if it sounds like a crazy person, if I am home or in the car alone, I will try to say what I am doing or plan to do in Portuguese. If I don't know a specific word, I still try to get the overall concept. For instance, let's say I am driving to the grocery store, so my sentence might be "I have to go to the grocery store." I don't remember the word for grocery store, but I know how to say "Eu tenho que ir." It may not be perfect, but it's practice, and the more you do it, the better you will get at it. Plus, if I really want to know the word for grocery store, I'll look it up when I get home.