Anyone can stream their gameplay in real-time for the world to see. Aim to build a large audience (which you can monetize with ads) or a loyal audience (to monetize with donations and subscriptions). The biggest platform for streaming is Twitch, but YouTube is also an option.
Win Gaming Tournaments and Acquire Sponsorships
2.Tournaments are commonplace for PvP titles, like fighting games. Of course, the more popular the game, the larger the prize pools become. If you're skilled enough to join an esports organization, you may be able to earn a livable salary through winnings and sponsorships. Most competitive gamers also take advantage of live streams (#1) for additional income.
Get Paid to Test Games
Games go through various phases of development before they're released. Near the time of completion, developers need outsiders to playtest their games with fresh eyes. As a playtester, your job is to check over everything the developer wants you to look at, which includes finding and documenting bugs and other issues.
Sell Accounts or Digital Items
If you've spent enough time in some games, you might be able to "flip" your account or in-game items to other players. As one example, you can resell some Steam Trading Cards earned by playing games to players who want to collect them. While you won't make huge money from this, you might be able to earn enough to cover your next game purchase.