To start out, I would recommend looking for podcasts designed for English language learners. The British Council has good ones as does the Voice of America. Podcasts or videos with transcripts are the best, however, try to listen without reading first and listen to each podcast several times. To be the most beneficial, the podcast should be comprehensible, in other words you should be able to understand most of it but not all. Once the podcasts designed for language learners start becoming easier, start watching some English language movies and TV programs as well.