This
is one of my favorite techniques for really keeping the
tension on the shoulders when doing dumbell shoulder presses.
The action is really simple...rather than doing both dumbells
at the same time (as you would in a normal press), and
rather than holding one dumbell at the bottom while you
press the other one up (which dramatically decreases the
amount of weight you can use because the bottom is the
toughest position to press the dumbell out of), you will
instead hold one dumbell at the top while you lower then
press the other one!
I
learned this one from the late, great Vince Gironda (not
personally, but in his writings). It's a great technique!
So
basically, you start with both dumbells in the lock-out
position.

Now
you lower the right dumbell:

Then
you press it back up to the top:

Now
you lower the left dumbell:

Then
press that back up to the top!
That's
pretty much the whole deal. It does take a bit of practice
to get the coordination flowing smoothly but I've found
it to be extremely effective for working the shoulders.
It keeps great tension on the delts and I've even found
(after working this one awhile), it allows me to press
more weight than when I try and to do both dumbells at
the same time.
The
reason for this is that the neurological impulse to the
work muscles aren't split between two limbs but instead
just go to one side. This gives you a bit more strength
to work with when you work one side only.
Give
this one a try in your next shoulder workout and check
out the video to see the reverse alternating style in
action.