William Lilly's epistle paraphrases/modernises thus:
My friend, whoever you are, to whom I offer the benefit of my studies if you wish to learn about the Stars, in which the great and glorious design of God is so manifestly apparent,
In the first place, be thankful and humble before God, and never allow any science (however profound it may be) to distract you from the fact that Divine Providence governs everything; the more you learn, the more you understand the power and wisdom of Almighty God and strive to be in his favour, the more reverent your approach, the more accurate your astrological judgement will be.
Beware of pride; remember that long ago Man lived in harmony with his world, but when Man exerted Man's Will on the world he found it to be unmanageable. Remember that the Universe was created in harmony, and Man is part of that harmony : Man is Spirit manifested. Be worthy of the gifts bestowed on Man by God, and forswear trivial pleasures. Once you have contemplated God and your Self, this is how to conduct yourself.
Be humane, courteous, open and available to all.
Mitigate harsh pronouncements with gentle advice and direction to the Grace of God.
Keep the company of modest, civil, learned, sober people.
Covet nothing, and give both money and judgements freely to the poor. Do not let wealth influence your predictions.
Be prudent when pronouncing on your society. Do not contemplate the fate of the Leader.
Marry someone with a similar outlook, treasure your friends, avoid controversy.
Study hard, so you become an expert at your art.
Don't be extravagant, rather focus; have faith and resolve, betray no confidences.
Instruct all men to Live well, and be a good example yourself.
Avoid the fashions of the times.
Love your country.
Judge no-one, not even an enemy.
Don't be dismayed if people speak ill of you, let your conscience be your guide.
WILLIAM LILLY. 1647 [paraphrased, with respect, E&OE]
You can see the original here.