Long time lurker here, so here is how I pick an online casino these days. After getting burned once or twice I learned to read the small print first.
First thing is the licence: see which authority is listed in the footer, and if your country is on the allowed list. Then payments: I want at least one fast e-wallet option, and the withdrawal limits need to be written clearly.
The welcome offer is where most people get caught. Anything above 40x rollover is a red flag for me, and the bonus usually expires in a week or two. A useful overview with bonus rules, app info and payment methods is worth a read here just casino app so you know what you are signing up for.
On mobile I mostly use the browser version, so I check how the lobby works on a small screen. Test the live chat before depositing: if they answer in a couple of minutes that is a good sign.
Anyway, that is my routine. Only play with money you can afford to lose.