How do you make a viral Youtube video

You don't try, it just happens.

First thing you have to do is not suck.

Use me as an actor.

You have to make something that's a popular subject, that people can relate to. But you have to do so in such an extremely high quality and well made form, and in a unique way so people stay interested. Be funny, creative, and make it look amazing. Then advertise the hell out of yourself. Whatever topic you're doing, post to any sort of forum on the internet that relates to that topic. Viral videos don't happen out of thin air, especially when you're trying to make a viral one.

• You need to offer something that people want, but can't already get in a more popular channel.
• You need a quality video, which is entertaining, well made and has been edited to cut out the guff.
• You need a reason for viewers to continue watching your videos.

Failing all that, just film hundreds of cats doing random stuff.

video tape a cat. boom a million views

try something never done before, or conbinations that are so random and funny.

take example thug notes

Cat videos and tits D:

As in many other things, if this is your goal then probably it would not happen, you should make a video for yourself(meaning the you like it) and that you think other people may like. Just don't try to make a viral video, try to make a good/fun/etc video instead, the rest will come eventually.

edit: just another thing, look for something different, if a field is saturated don't be the generic person that make the same thing cause he see it worked for others and that may be safe, there are already million of other people with the same way of thinking; instead think outside the box make something innovative/different that the people may be curious to watch, try the most absurd things, even if they may bring hate on you (risking is good and in this field there is not so much to lose) at least you managed to get viewers from that point you can reach people more easily.
In the end: i don't know what i wrote, my comment is stupid.

Viral videos happen with luck, but to get a steady viewer base you should upload consistent and preferably original content.