There are two points on how to prepare for playing in an online casino: firstly, you need to prepare psychologically and perhaps this aspect is extremely important, and this can be helped by watching online interviews with addicted gamblers, as well as reading the gambling discution thread here, where a lot of useful advice is given for gamblers, because here it is discussed how not to become addicted and not get into debt due to unsuccessful games.
The best way to prepare psychologically for gambling is to understand it well and to do things right. When people gamble beyond their means, it will definitely affect them psychologically.
If you want to be free from gambling-related psychological issues, you just need to do the right things, such as managing the amount of money used in gambling, tracking the frequency of gambling, and understanding the uncertainties involved. If these things are understood, then I believe one is well prepared to engage in gambling.