1: Guard Clauses

Code like this:

if(condition)
... some code ...

Or like this:

if(condition)
    if(not other condition)
        ... some code ...

Tidy the code above to something like this:

if(not condition) return
if(other condition) return

... some code ...

As a reader, it's easy to get lost in nested conditions.

Code with guard clauses is easier to read & analyze because the preconditions are explicit.

Don't overdo guard clauses - a routine with sever or eight clauses is NOT easier to ready.