There are 2 different methods. The first method, which is easy but can get messed up on a poor internet connection, is to simply stream the file from the server via HTTP. Before you can do this, you have to enable automatic extraction in the client you're using (I dunno about the other clients, but in rutorrent it is under 'Settings'>'Unpack'>'Enable auto unpack'). The unpack should be almost instant, or at least very quick. Next, you have to go to the HTTP part of your seedbox. After this, copy the link to the extracted file, and open VLC. Once there, click cmd+n or ctrl+n and paste the URL you just copied. You don't need to mess around with the settings, just click enter. After this, you'll have to type in your username and pass (the same one you use to access your HTTP server thingy), and hit enter. That's all! But you must be careful, and not pause it for more than a couple of seconds, otherwise it looses the connection (at least for me it does), and you'll have to restart the stream. This can be problematic, as it doesn't always allow you to go forewords or backwards.
The second method I use is not exactly 'streaming', but it allows you to play the file instantaneously nevertheless. I do exactly the same thing as above, but instead of copying the file URL, I just download it. It will look like a corrupt file in Finder (or windows explorer), but it is in fact playable with VLC. If VLC tells you that you need to index the movie file, just tell it to ignore, otherwise it will mess up the video. If you do it this way, you can go backwards and forwards within the video, and pause it for as long as you want. If you have a fancy downloader, you can even resume the file if you got disconnected or something. It works great, and then you can also have the actual file in the end. The only problem is that VLC crashes if it reaches the end of what you downloaded faster than you've downloaded the file. This sometimes happens when I try to 'stream' 1080p movies, and on a slow computer it can be a problem, so keep this in mind. Usually, if you let it download, or 'buffer' for a couple of minutes before playing it, whilst you get a sandwich or something, you should be fine.