Safety comes first
Standing water can create electrical and contamination hazards. Do not enter water where electrical equipment may be energized. If flooding may involve sewage or another contaminated source, use appropriate professional cleanup help.
After the water is removed
Document where water entered, whether the sump was operating, whether the flooding followed heavy rain, and whether wall cracks or perimeter seepage were visible. Those observations are much easier to make before everything dries.
Preventing the next event
Possible prevention work may include sump or drainage improvements, crack repair, better exterior water management, or a broader waterproofing system depending on the cause.