Use 'sociably' when highlighting enjoyment and ease in social interactions, especially informal ones. After the game, the players mixed sociably with the fans.
Pro Tip 2/3
Not Alone
'Sociably' suggests the presence of others; it's not used for someone being friendly by themselves. She didn't enjoy alone time and preferred to dine sociably with friends.
Pro Tip 3/3
Positive Interaction
It implies positive interaction; avoid using 'sociably' for scenarios where there is tension or unfriendliness. They were arguing at first but ended the night talking sociably over coffee.