This is a multipart series - your comments and interactions are always appreciated.
Testimony? Sounds like I'm in a court room... "A formal written or spoken statement, especially one given in court;" is one definition but in this case "a public accounting of a religious conversion or experience," is what people are addressing when using the term "testimony."
Commonly a testimony refers to a specific event in a Christian's (Saint's) life in which God did something deemed particularly worth sharing. Many times the sharer may mention that they are giving the testimony in order to "give God the glory." They are sharing what transpired and likely an answer to pray or subsequent events in which God intervened on behalf of the sharer or they are recounting it on behalf of someone else. The purpose of telling it is not only to inspire fellow Saints but to publicly thank God for his help and mercy in the situation.
I thought it good to shew the signs and wonders that the high God hath wrought toward me.
A testimony has a point. Keys to a good testimony include brevity; only filling in various and sundry details that help provide context to your narrative. Sincerity, a desire to tell others what a mighty God you serve and not a recitation of one's own knowledge, skills or abilities that distract from "giving God the glory." And most of all inspired by God.
There is no small or grand testimonies, if God has inspired you to share something with others that lift him up and point others to Christ who are you to determine whether the testimony is too insignificant to share.
Lastly if God has inspired you with a testimony it always helps to prepare. Notes are not a bad thing, they keep you focused, concise and prompt you not to forget anything. A good testimony when delivered effectively leaves the hearer rewnewed in heart and recharged in their conviction that God has an answer for them as well.