A discussion on how to become an expert in the game of roulette is bound to be met with skepticism in certain quarters. That is understandable, because roulette is largely viewed as a game of chance. People typically talk of 'expertise' when dealing with games of skill. But when we are looking at games of chance, such as roulette, the idea of being taught how to become an 'expert' is bound to be met with some skepticism.
It is indeed true that one of the major determinants of success (or failure) in roulette is luck. As such, roulette qualifies to be described as a game of chance, rather than a game of skill. But you also come to realize that in these games of chance, there are still some rules which need to be subscribed to. Proper knowledge of these rules is what makes the difference between the folks who consistently win roulette games, and people who consistently lose in roulette.
The rules governing roulette can be seen as falling into two categories. In the first category, we have basic game rules which govern the actual playing. These are rules you have to subscribe to, if it is to be said that you are playing roulette. In other words, subscription to these rules won't make you a roulette expert. It only makes you an ordinary/proper roulette player.
The second category has rules which, when applied, can increase the probability of winning. Some people prefer to view them as rules which minimize the probability of losing. You don't have to know these rules, to be termed as being a roulette player. But knowledge of these rules is likely to give you an edge over other folks, who only know the basic rules of the roulette game, but who don't really know these advanced rules of roulette.
To get an idea on the relevance of the advanced rules of roulette (whose knowledge is bound to make you a roulette expert), we need to have some basic appreciation of roulette. That is where we will come to learn, as mentioned earlier, that roulette is a game of chance; specifically, a betting game. In roulette, you bet against the house (unless you are playing in the tournament format, where you may get a chance to bet against other players). The casinos which offer roulette are, of course, in business. To ensure that the roulette venture remains profitable, they see to it that the game is designed in such a way that, for any given bet, their chances of winning are higher than yours (as the player). The degree to which their odds of winning are higher than yours is referred to as the house's edge. It emerges that for every particular move you make when playing roulette, you vary the house's edge.
There are some moves you make, and instantly raise the house's edge (and with it, your chances of losing). There are other moves you make, and instantly lower the house's edge (and with it, your chances of not losing). It is only when you gain perfect mastery of the rules governing those things that you are said to have become a 'roulette game expert.'
In a nutshell, to become a roulette expert, you need to study all the available body of literature on roulette strategies. You need to develop your own strategy, from all that you learn through such literature. You need to practice and refine that strategy (ideally, through low stakes roulette games). It is the consistent application and refinement of the roulette strategy developed that way which will make you a true, roulette game expert.