High Valyrian sounds interesting but the problem is that their is no sound for the course. And barley any tips. The course needs to have more work on it because High Valyrian grammar is very hard.
There are plans to add sound at some point but it is a language that is still under construction so just be patient. If you want to study the grammar and pronunciation in more depth I would start with these websites https://wiki.dothraki.org/Main_Page and here is one with David J Peterson's own pronunciation http://www.makinggameofthrones.com/production-diary/2014/5/8/high-valyrian-101-learn-and-pronounce-common-phrases I would use those as guides rather than the tv show if you want to sound more natural