I play mostly 4v4 games (as random with random people) and I'm stuck in the gold league with 765 wins. I'm looking for any guides or tips, how to progress in 4v4. Progamers usually stream only 1v1 games and the majority of tutorials are dedicated to 1v1 as well. Are there any tutorials focused on teamplay?
4v4 games are considered "fun" games, so usually everybody tries to cheese somehow. The game is definitely not balanced for 4v4s.
You should stop playing this mode competitively and go for 2v2 if you really like team games.
The problem with huge games like 4v4 is that there are way too many permutations to consider. In 1v1 there are 3 matchups you have to learn, if your race remains the same. In 2v2 there are already 6 or even more if you play random team. You get the idea.
But if you really want to progress in 4v4 here are some tips:
Learning something new works best like this:
Most of the 1v1 mechanics work also in 4v4.
To be a better player means to be able to play reactively to the situation in the game. In 1v1, this means scouting your opponent and preparing for what's coming, or playing more greedy because you know you can get away with it. In 4v4, knowing what your teammates are doing is almost as important as knowing what your opponent is doing. Fortunately you have complete vision of your teammates, and thus playing "reactively" in 4v4 is much easier. This will make you a better teammate, and give you some control over your success in random 4v4.
It can be annoying to cooperate with bad players ("battlecruiser rush" for example), but in the interest of winning, it's necessary to swallow your pride and proactively carry the game for your team.
4v4 is extremely volatile, where luck is more of a factor than skill (getting good teammates, chemistry between teammates, map positioning, 4v1 rushes...). If you want to have control over your success, you should stick to 1v1, 2v2, or make a predefined 4v4 team with 3 friends (instead of having random teammates). I honestly don't even know how battle.net can give an accurate MMR for the 4v4 format.
1v1 is really the place where you improve as a player though. If I were you, I would play 1v1 to get better, and 4v4 to put that skill to use. Maybe set a rule for yourself, like you always warm up with a couple 1v1 matches before going to 4v4.