I advise to an inward waiting upon thy gift, to feel the moving thereof in thy own mind, which will by a gentle illumination clear thy understanding and judgment, whereby thou wilt clearly see thy place and service in the Church; and if thou findest it thy place to minister to others, be willing to do thy Master's will, and stand up in the meekness of the spirit which moveth on thy mind, and speak the word thereof according to the present opening that is before thee, regarding strictly on the one hand, by speaking too fast and too loud, thou do not over-run thy natural strength, gift and opening, which, if thou happens to get into it will bring thee into confusion, and thou wilt not know when to conclude, and so mayest shut up thy own way in the minds of thy brethren, and bring thyself under a just censure; therefore whenever it happens so with thee, sit down; for by endeavouring to mend it, thou mayest make it the worse. So on the other hand, be not too low, nor too slow in thy speech, so as to lose the matter that way; but carefully keep to thy opening, avoiding both the extremes. Stand up in a calm and quiet frame of mind, as free as possible from either a fear or care how thou shalt come off; but follow thy guide in all circumspection and humility, beginning, going on, and concluding in thy gift. Thus wilt thou experience, what the wise man said to be true, “A man's gift maketh room for him, and bringeth him before great men.”
-- Samuel Bownas, "A Description of the Qualifications Necessary to a Gospel Minister"
In another passage, he warns against superfluous words and gestures (holding one's arms out wide, or gazing upwards). I don't see these gestures much, but it sure seems like people throw in a lot of extra words. Someone might give a long description of how they came by a particular book, as well as a professional history of the author, before quoting a short passage. It is one thing when details seem extraneous at first but then tie in at the end, it is another to provide details that have nothing to do with what one is trying to say.
Bownas also warns against "borrowing", using things we have read or heard as a substitute for what is given by the Spirit. I love the manna metaphor used here:
But the danger of borrowing may lie as near, respecting the scriptures of the Old and New Testament, with any other books that may affect our minds, as what we have heard delivered in the openings of life. For it is no more lawful for us to preach what we have read, because we have read it, than it is for us to preach what we have heard, because we have heard it. Nay, I may further add (what thou wilt find by experience true in due time) that it is not lawful for thee to repeat thy own experience, and former openings, merely in thy own strength of memory and will; for if thou dost treasure up and furnish thyself this way, thou wilt be greatly disappointed, and thy doctrine will be like the manna kept out of season; worms bred in it, and it stank. Now a spiritual minister is, and ought every day to be, like blank paper, when he comes into the assembly of the Lord's people, not depending on any former openings or experience, either of his own or others, that he hath heard or read; but his only and sole dependence must be on the gift of the spirit, to give, and bring to his understanding matter suitable to the present state of the assembly before him.
A couple of lines from Proverbs 30 came to me this morning while reflecting on Bownas:
Every word of God is pure: he is a shield unto them that put their trust in him. Add thou not unto his words, lest he reprove thee, and thou be found a liar. (Proverbs 30:5-6, KJV)
I have often heard verse 6 quoted in reference to biblical translation and accuracy. I had never before considered it with respect to vocal ministry, and now that I do, they really shine for me - that I should strive towards speaking only those pure words from God, not adding my own.