I want to get better on Down picking, since im playing much Metallicalike songs.

How do I practice this best? is it just play much downpick-songs to improve or is it a better way?

I have only found one lesson about this in the lesson section
Find yourself some chugga-chugga Death Metal like Eaten from Bloodbath. Best downpicking powerchord song for a beginning player. You can speed it up if you like, the song itself is fairly slow. Also in A standard but tuning the Gp5 that's on this site up isn't a problem really.