Pretty much everything you ever hear I've done or tried. Reddit is extremely good however you need to spend time building up karma. Sharree and drummitup are excellent (google them if you don't already know them). Without a doubt the best way to get subscribers is to really spend time working on a community and we have a really great massively growing group where about 5 of us do shoutouts regular and that is really acknowledging the other members that are putting in the work and time supporting other channels. What usually happens there is that everyone else checks out their channel and it often leads to subs, comments, likes, etc. This is not a sub for sub by any means, but by visiting round the channels, watching their content, commenting, etc it often brings more people to your channel and you will start to see familiar names. I have made some fantastic friends.
A small example of how this has helped me just this week. I'll use person A and person B for the example. Person A gave Person B a shoutout and through that shoutout I visited Person B's channel and was impressed with it so I introduced myself and told him that I found him through Person A's shoutout. Long story short, Person B then visited my channel and similar subbed, he also asked me if he could do a collaboration which I agreed to. He only posted it yesterday and I think I've gained 5 subs already. These are not just numbers though, I interact with them and usually (if I have time) visit their channel and check it out, if I like it I will also sub and honestly it just creates a snowball effect. Anyway I will now post the collaboration video on my site and hopefully it will interest some of my subs to visit his channel.
Not too much different from the forums here, you eventually start coming across familiar names and 'get to know' people. Anywhere you go online you need to become a part of the group so to speak, there is nowhere magic you can do a link dump and expect a massive rush of views, no matter how much talent you have, you need to be seen and the only way youtube starts showing your videos is when they see activity on them, comments are super important. Lucky I'm a massive chatterbox (in case you didn't notice). Anyway I hope that all makes sense, look me up on yt (granny gamer) and you will very soon see exactly what I mean as I have also started doing weekly shoutouts and I'm always nattering on about building the community