One of the easiest ways to increase your subscribers is by simply asking your viewers to subscribe to your videos. Don’t assume that the viewers can read your mind and do it. There are some that will automatically subscribe if they enjoy the content, but most people are more likely to do it when reminded if they’re enjoying the content.
You also have to get your timing right when asking the question, it wouldn’t make sense for you to ask them to subscribe at the beginning of your videos without them watching any part of your content, as they don’t see any point in subscribing to your channel at that point. Hence, try to time it so you don’t distract them at a good point, but at the same time you don’t want to ask them at a point where it is boring. Try to time it so that you can ask them after a fun subsection of your video is complete and before you go to another scene. This way, because they’re enjoying your content at that point, they’re more likely to interact with it positively and subscribe.