Going deeper is safest when your supporting systems improve at the same time. Depth alone is not enough if oxygen, navigation or power remains the real bottleneck.
Create more breathing margin
More time underwater makes route learning and resource decisions less rushed.
Make the return route obvious
Markers and recognizable paths reduce the chance of turning exploration into a navigation emergency.
Check food, water and power
Longer trips magnify small supply problems that would be harmless near the base.
Use the first deep trip to learn the area
Do not try to maximize resources before you understand the route and hazards.