Flatten nested if statements with the opposite condition

Have you ever found yourself nesting if, for and other flow-control statements seemingly endlessly into the dreaded arrow formation?
EG:

if this:
    if that:
        for x in X:
            if yuck:
                ...
            else:
                ...
                continue
    else:
        while Y:
            if foobar:
                ...
            else:
                ...
                break
else:
    ...

One of the easiest ways to collapse if statements is using the opposite condition and return, continue or break.
EG:

if not this:
    ...
    return
if not that:
    while Y:
        if not foobar:
            ...
            break
        ...
    return
for x in X:
    if not yuck:
        ...
        continue
    ...

Some refactoring tools will help you do this, but it good programming practice to avoid nested flow-control statements when possible. Even though in this case it only eliminated 2 lines, it is more compact, lines are not as long, so wrapping/continuing/splitting commands is not an issue, and in general the code should run faster, since it only executes as much code as is needed before returning, continuing or breaking.