You don't. In gambling, everybody has only one level. There is really no point in getting a lot of experience in it as the changes are basically the same across the board.
So "leveling up" is basically a stupid concept in the world of gambling.
Exactly, if you have the mindset of leveling up right from the onset then I bet you'll never be successful at gambling. It can even land you in serious addiction if care is not taken so I will suggested you be as modest as possible before you gamble and never imagine leveling up.
The OP are pertaining to become experienced gambling on his word of "leveling up" and you misunderstood it by thinking that it is the level up concept on a video game.
Leveling up or being an experienced gambler is existing on gambling world. It will take time and money in able to learn and experience different kind of situation that will help to level up your gambling skills.