When I first began doing Shoutouts they were for people like Jardine 64 (now Roguebluejay) Crabstickz, Delanewazhere, Stewze and others. I enjoyed their videos and thought others might too. These days I am loaded with requests and suggestions to put at the end of each video. To be honest I was considering dropping the Shoutouts at the end. But instead, I'll start selecting each one again.
Many state that they'd like more subscribers. Here's the flaw in the thought. I can draw them to your channel, but your videos have to interest the viewer and motivate them to subscribe.
Here's how I got more subscribers. I became involved in other channels by commenting and rating. You'll need to be positive in your comments and video reply making sure your video relates to the topic. YouTube is all about community. And, don't forget to be yourself. We all love to watch people being who they really are.