There are two ways to earn this achievement. One will be from playing high stakes poker in Blackwater, the other will be to go all in while completing the mission "Lucky in Love". Your aim will be to win 2,000 chips in a single pot. Raising the pot against the AI is very time consuming; you will also need to know the game inside and out to be very successful.
Before you can access Blackwater you need to complete Act 2 so you can access The North. High Stakes Poker will allow you to place bets than exceed any limit elsewhere in the game. Before you take part in these games you may want to buy the Elegant Suit from the Tailors shop in Thieves' Landing.
If you're not so good with card games but want to learn you can follow this tutorial and teach yourself how to play.
Mexico, Lucky In Love:
If you're not so good with card games but want to earn this achievement with ease you can try and trick the AI in the mission "Lucky In Love". You will be given this mission by Landon Ricketts as you progress through the story. As you sit down to play the game you will start with 1,000 chips. Go all in with 1,000 chips, at this point some players may bet or fold. Once you win, repeat the same bet again. If you're successful you will win 2,000 chips and the story will continue.
This method doesn't always work the first time. You may need to reload a previous checkpoint or save and try again. If all the players fold you won't win the full 2,000 required.
You will find poker games in the following locations: