The best advice I can offer you is to try to eliminate music from meditation. Of course, everyone has there own way, and I'm a not a fan of strict rules when meditating, but listening to music to while meditating can severely defeat the purpose. The essence of meditation is nothingness. Even though you may be able to achieve a meditative state while music is playing, you will be doing it in spite of the music, not because of it. Now, music can be helpful for relaxing, and to prep yourself for a meditation session, but I don't think it should be use while meditating.
As far as literature, it depends on your meditation style or philosophy. There are different types with different methods. You mentioned that you use deep breathing techniques, so I would suggest looking for literature on mindfulness Vipassana meditation. There are many schools of thought on meditation, so I'm not sure if you are looking to follow a certain discipline or not. Personally, I don't follow a certain technique. If I experience something interesting, odd, or intriguing during a session, I might seek out some literature on that particular phenomena. I do it that way because I don't want to get bogged down by a certain philosophy. I do read Tao and Buddhism books, but more for philosophical purposes instead of meditative ones.
Meditate as long as it feels natural. With more practice, the longer your sessions will become. Never force yourself to meditate longer. As far as posture, just do what works best for you. I actually prefer to lay straight on my back, as if I'm going to sleep. I am most comfortable that way. I also will meditate Indian Style, just to switch it up, but I prefer the laying style. You can even lay on your side to meditate. It's all about being comfortable. But I do think you should switch it up every once in a while for the sake of variety, plus, I do believe that energy can flow in different ways dependent upon your positioning.
The best tip I can offer is to quiet the mind, which will lead to more productive, and longer meditation sessions. If you find yourself thinking about something during the day, immediately dismiss the thought. Constantly do that every time a thought pops up, or when dialogue is happening in your head. This is called eliminating mind chatter. After a while, you will realize that your mind is much more clear, and you will become more relaxed. This will greatly improve your meditation. Meditation will also help you improve eliminating mind chatter, so the two have a symbiotic relationship.
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