I treat the use strict; and use warnings; declarations as a way to document the beginning of the actual code. I therefore put them immediately after all my other use statements and obviously after the package statement as well.

use MyTest qw(mysub);

use strict;
use warnings;

my $foo = 'bar';

mysub($foo);
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This serves no purpose. The code would work the same if the strictures requirement was placed sooner.

I believe sometimes people put them later because they are lazy about their @EXPORT declarations, and don't always use our.