There's loads of variables that comes into play when you gambling online. Most still regard gambling as a vice or seed activity.
Make sure the casino where you're about to play at is licensed in a credible jurisdiction. Jurisdictions such as the UKGC (United Kingdom Gambling Commission), Malta, Alderney, Gibraltar and Curacao.
The casino must offers a large selection of games by different software providers, offer new players a sign up bonus with attainable wagering requirements, cash back on losses to regular depositors, must award comps on certain games and a VIP program.
The most popular games on the casino's floor are: slots followed by table games, video poker and progressive jackpots. Before you play an online slots study its paytable first, it most offer a payout ratio of more than 96% and loads of in-play bonus modes (free spins, wild substitutions, scatters and multipliers).
Last but not least the casino must clear cash outs fast-this is not negotiable. The last thing you want is to wait for your cash for more than 5 days. That said, the withdrawal time frame also depends on the deposit method you've used. You can fund your account with Bitcoin, credit cards, ewallets (Skrill or Neteller). But to me Bitcoin is by far best deposit method. Reason being you're not tied down by the casinos' low daily or weekly withdrawal limits, cash outs are virtually instant and you can withdraw up to $90,000 per transaction.
I can go on and on but I've just covered the points I deem important.