Just for today, do not anger
Just for today, do not worry
Show gratitude to everything
Earn your living honestly
Be kind to every living thing

The original document as written by Dr. Usui:
'Shoufuku no hihoo
Manbyo no ley-yaku
Kyo dake wa
Okolu-na
Shinpai suna
Kansha shite
Goo hage me
Hito ni shinsetsu ni
Asa yuu gassho shite kokoro ni neji kuchi ni tonaeyo
Shin shin kaizen, Usui Reiki Ryoho
Chosso Usui Mikao'

Direct translation is like this:
Just for today (Kyo dake wa):
Don't get angry (Okoru na)
Don't worry (Shinpai su na)
Be grateful (Kansha shite)
Work hard (Gyo o hage me)
Be kind to others (Hito ni shinsetsu ni)

Just for today, do not anger
Anger creates serious blockages in our energy body. We generally get angry when our ego gets hurted. If we discard our ego and try not to be angry, the Earth will be a better place to live.

Just for today, do not worry
We are generally afraid of facing the unknown. Future is unknown to us, that is why we worry about the future. Excessive worry damages our courage to move forward and face the uncertain, thus causing emotional blockages.

Show gratitude to everything
We can not live alone in this world. We are a part of the Biosphere or the Universe or the Oneness.

Earn your living honestly
Honesty give us courage to face anything, thus brings abundance in our life and generates peace in our mind.

Be kind to every living thing
Compassion or 'Karuna' is the greatest virtue.

Related Links:
The Five Reiki Principles in Japanese
The Gokai - Reiki Principles
Variations of Reiki Principles