Reddit is full of trolls, you don't want to build a toxic community which is why I don't intend on using it to promote my channel. The aim of the channel should be to build a loyal viewer base so word of mouth is definitely the best way of promoting it. It all depends on the niche of course however start from the ground and build up.
If you have a comedy channel for example, ask your friends to subscribe and be active on the channel. Message them privately as they're more likely to take action. Sharing on your timeline gets missed easily and people don't tent to pay attention. However it's important not to randomly just pop up with a link, unless you're really close friends, have a genuine conversation - ask how they are etc. Then politely ask if they don't mind subscribing. Putting in that extra effort will get a lot more results.
That's the ground level. Build the next level by asking your closest friends to do the same thing to their friends. Feature them in a video, it'll give them reason to promote the channel. Getting two or three friends to do this will expose you to more people. If each of them ask 20 people, that's 60 people you wouldn't have been able to target.
Once you've done that, it's all about creating good content. If it's a comedy channel, upload a hilarious video, spend hours on it if you need to as that video will be crucial. You have a new audience who will be notified of the upload and click on it to watch - if they find it funny, they'll share it with their friends. Their friends will then share it with their friends. The chain goes on. It's also really important to ask them to share - in the middle of the video, spend 20 seconds asking people to share and subscribe. Call to action will remind people to take action.
Now you can focus on putting out good content and sharing it on your social media channels using your usual methods, in the off chance someone new stumbles across it and checks it out.
I've started on the very first base - asking my friends to personally subscribe and be active when I do upload videos if they enjoy the content. That's how I've got 9 subscribers already without posting a video and I've only asked 9 people. I've got a lot more promoting to do myself!
Good luck!