Often nested conditions can be rewritten as flat conditions with and:
# Nested version
if has_ticket:
if age >= 18:
print("Welcome")
# Flat version
if has_ticket and age >= 18:
print("Welcome")
Both do the same thing, but the flat version is easier to read. The and makes it clear both conditions must be true.
When you catch yourself nesting, ask: can I combine these conditions? Sometimes nesting is clearer (especially with else clauses), but often flat is better.