These are probably going to be repeats of what other people have said, but:
1. Add some comedy to your videos.
2. Get a decent gaming PC, nobody likes to watch a game run at 15 FPS.
3. Try to do some lesser known games. Some people (talking to you, Pewdiepie fans) will shoot you down saying you "copied" someone if you do some famous game.
4. Try to play with friends as much a possible. More friends, more fun.
5. Listen to suggestions from your viewers. Who knows, they might have a game you'd really like, or a cool new feature to the channel.