1.

Dead flies cause the ointment of the apothecary to send forth a stinking savour: so doth a little folly him that is in reputation for wisdom and honour.

This verse is by its meaning so closely connected with Ecclesiastes 9:18 that the selection of it for the beginning of a new chapter seems unfortunate.
Apothecary - Rather: a dealer in spices and perfumes (compare Exodus 30:25). The swarms of flies in the East very soon corrupt and destroy any moist unguent or mixture left uncovered, and pollute a dish of food in a few minutes.
So doth ... - literally, more weighty than wisdom, than honor, is a little folly.

2.

A wise man's heart is at his right hand; but a fool's heart at his left.

The metaphor perhaps means “A wise man’s sense is in its place, ready to help and protect him; but a fool’s sense is missing when it is wanted, and so is useless.”

3.

Yea also, when he that is a fool walketh by the way, his wisdom faileth him, and he saith to every one that he is a fool.

“Way” may be understood either literally (compare Ecclesiastes 10:15), or figuratively, of the course of action which he follows.
He saith ... - He exposes his folly to every one he meets.

4.

If the spirit of the ruler rise up against thee, leave not thy place; for yielding pacifieth great offences.

If the spirit ... - i. e., If he is angry.
Leave not thy place - i. e., Do not lose thy self-control and quit his presence. Gentleness on thy part will calm both thyself and him, and prevent great wrongs being committed by either.

5.

There is an evil which I have seen under the sun, as an error which proceedeth from the ruler:

6.

Folly is set in great dignity, and the rich sit in low place.

7.

I have seen servants upon horses, and princes walking as servants upon the earth.

8.

He that diggeth a pit shall fall into it; and whoso breaketh an hedge, a serpent shall bite him.

9.

Whoso removeth stones shall be hurt therewith; and he that cleaveth wood shall be endangered thereby.

10.

If the iron be blunt, and he do not whet the edge, then must he put to more strength: but wisdom is profitable to direct.

11.

Surely the serpent will bite without enchantment; and a babbler is no better.

Rather: “If a serpent without enchantment (i. e., not being enchanted) bites, then there is no advantage to the charmer”: i. e., if the charmer is unwisely slack in exercising his craft, he will be bitten like other people. See Psalms 58:4 note.

12.

The words of a wise man's mouth are gracious; but the lips of a fool will swallow up himself.

13.

The beginning of the words of his mouth is foolishness: and the end of his talk is mischievous madness.

14.

A fool also is full of words: a man cannot tell what shall be; and what shall be after him, who can tell him?

Full of words - Confident talking of the future is indicated rather than mere loquacity. Compare James 4:13.

15.

The labour of the foolish wearieth every one of them, because he knoweth not how to go to the city.

The sense is: “The fool wearies himself with ineffectual attempts, he has not sufficient knowledge for the transaction of ordinary business.”

16.

Woe to thee, O land, when thy king is a child, and thy princes eat in the morning!

17.

Blessed art thou, O land, when thy king is the son of nobles, and thy princes eat in due season, for strength, and not for drunkenness!

18.

By much slothfulness the building decayeth; and through idleness of the hands the house droppeth through.

19.

A feast is made for laughter, and wine maketh merry: but money answereth all things.

20.

Curse not the king, no not in thy thought; and curse not the rich in thy bedchamber: for a bird of the air shall carry the voice, and that which hath wings shall tell the matter.