Work against gravity on both the directions

In the GYM, most of the folks lift the weights slowly and put down the weights fastly.
Because, while lifting, they are working against the gravity and
while lowering down, they are working with the help of gravity.

This doesn't efficiently work out your muscles.

Instead of this routine, lift/push the weights at greater speed and
lower the weights slowly.
When you lower the weights slowly, the muscle provides the resistance against the gravity.
This is the efficient way to workout if you really want to improve your muscle mass.
Otherwise, you will not see much improvement.