Could you please say how you usually wish somebody to have a good meal when you are sitting at the table and are just starting to eat?
It's difficult for someone used to the Bon apetit / Buen provecho tradition to not say anything in this situation, but where I grew up speaking English (southeastern Pennsylvania), it is normal to not say anything, and there is no customary formula.
"Enjoy your meal" or "Enjoy" is something a waiter or waitress might say after serving, but not something I'd hear or say at the table with others. Maybe I might hear someone say it to end a conversation before leaving someone at the beginning of a meal.
Normal is simply to begin eating and have a conversation about anything. If you felt that you had to say something before you began to eat to mark the beginning of the eating, you might say "Let's eat." or "It looks good. Let's eat."
If you wanted to invite others to start eating, you could say "Dig in." (informal) or "Please begin."(formal)
English-speakers who have learned "Bon apetit" often say it (in French), because we don't have a corresponding tradition in English (at least in my community).