Having clear, non-predatory terms and conditions. Fast withdrawals, partnering with reputable and trusted game operators and having my preferred payment options. If they meet the above conditions then it comes down to their attitude towards players, helpfulness and personality of support operators, generosity with freebies and bonuses for active players and quality of promotions.
Seems like an easy task, but many more fail to meet the criteria than those who exceed it.
Having a community like AG or other respected gathering places of likeminded players to share experiences, problems and praise goes a long way in deciding who is even worth a first deposit.
WagerMan reacted to TheAverageGuy in Help choosing a casino