In my opinion, coming from someone that is a Doctor and part-time YouTuber with 3.3k subs
Here are my tips.
1. Your video content should be at least longer than 5 mins, and of course, some viewers are not into long videos, etc.
2. Upload videos every day or at least 5-6 times a week.
3. Know your audience, what I mean is., you should know what your audience what you to upload, etc.
4. Uploading schedule is really important and also play the latest or popular games.
5. Don't do subs4subs, I never do it nor believe in it, YouTube is not about how many subs you have, it's about your views (audience). The only reason you need subscribers is for the notification, whenever you upload, your subscribers will be the first to see your videos, click and watch it.
6. Not to prolong this list., make sure you join facebook, twitter groups or any gaming groups where you can share your YouTube videos.