For beginners: by the amount of times you caught your mind wandering (and brought it back to the meditation object), and also how many seconds it was wandering before you became mindful of it (the shorter the better). For long-term meditators: by the amount of time you keep at your meditation object without distractions and mental chatter. Your state of mind after your meditation finishes is also a good indicator of “how good was your meditation”.
But again, I wouldn’t encourage you to keep accessing your meditation sessions. It’s just more mental movement, and it doesn’t need to be there. It often creates more problems than insight.