I have settled on reducing horizontal indentation (code creeping across the screen) by using more vertical indentation.

if (
  condition1 or
  condition2 or
  condition3
)
{
  # do something
}
elsif (
  condition4 or
  condition5
)
{
  # do something else
}
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I like the top down feel this approach gives me.

As has been mentioned already, if the code does start creeping across more than, say, 3 'levels of indentation' it almost certainly means it'd be better off being rewritten. I can't hold that many levels of a process/sub processes in my head at a time.

I often take a similar approach to functions/objects. An extreme example:

open(
  my $fh,
  '<',
  'text.txt',
) or die "died";
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Down is better than across :-)