One common mistake that is made when assigning to a collection of scalars is this:

my ($one, $two, $three, $four) = 0;
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People tend to think that all four variables are initialized, but really only $one is set to zero, the rest are still undef. You'd have to explicitly set each variable to achieve that result:

my $one = my $two = my $three = my $four = 0;
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... or alternatively:

my ($one, $two, $three, $four) = (0,0,0,0);
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But as was stated elsewhere, this lacks readability for large collections of scalars. In general, I tend to declare my variables and either initialize them to zero or leave them undefined, then assigning their values in later statements. I hate getting warnings about variables being undef when evaluating in a conditional statement.

Just a quick addition to ptum's. I would write:

my ($one, $two, $three, $four) = (0,0,0,0);
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as

my ($one, $two, $three, $four) = (0) x 4;
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(undef, my $foo, undef, my $bar) = @array;
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my $foo = "ab";
(my $avar, $foo) = ($foo =~ /(.)(.)/);
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I prefer slicing. Instead of:

my (undef, $foo, undef, $bar) = @array;

or

(undef, my $foo, undef, my $bar) = @array;

do:

my ($foo, $bar) = @array[1,3];

e.g.

my ($size, $mtime) = (stat $filename)[7,9];