These are some tips that will help you get started (at least):
1. Record games that people watch. Don't record old games like COD 4, or some other game that nobody plays. Record games like Minecraft, Black Ops 2, Ghosts, Skyrim, Dark Souls 2, GTA 5, Watch Dogs.
2. Have good quality content. You should upload 720p or 1080p videos. If you are recording in console, buy a capture card (I would recommend the ElGato Gaming Capture Card). If you are recording in PC, buy a screen/game recorder (I would recommend Fraps or Dxtory)
3. Have good audio. You should get a good microphone like the BLUE Yeti or the BLUE Snowball. And also get a pop filter. If you don't want to spend that much money, buy a gaming headset with good microphonne. I would recommend the Razer Kraken Pro, the Razer Kraken 7.1, or the Astro A40 if you record in PC. If you are in console I would recommend the Turtle Beach.
4. Talk and be energetic. Almost nobody likes gameplay videos without voice commentary. And when you talk be sure to be very active. Don't be boring and sleepy.
5. Upload daily if you can. At least for the first 3 months try to upload 4-5 times a week. Even if you don't get many views in each videos, but with more videos you get more views, and with more views you get more subscribers. After you get like 100 subscribers, you can upload 3-4 times a week because you will now have more people that watch your videos.
6. Promote your videos and channels in YouTube and gaming forums. But DON'T spam. Don't publish the same post everyday. It annoys people. And DON'T advertise your channel in videos of famous YouTubers like SkyDoesMinecraft or CaptainSparklez or PewDiePie or Ali-A. Maybe you can do it once or twice in like a lot of time.
7. Collaborate with other YouTubers. Record videos together, do Sub4Sub or Like4Like or Box4Box. Everyone loves videos with other players.
Hope this tips help you get started.