The Bible's full of great preaching. It's also very honest about one sermonic failure: Acts 20:7-12 tells the story of Eutychus, who fell asleep when the Apostle Paul was preaching and fell out of a window.

I sympathise – with Paul, that is. I remember on one warm Sunday evening in my early years as a minister counting six people asleep during the sermon (not all at once). That was a low point and I hope I improved. I also remember being told by my college principal during sermon class to go and read CH Spurgeon's Lectures to my Students and pay particular attention to the woodcuts showing pulpit mannerisms: "You fall somewhere between the wrestler and the dancer," he remarked.

In evangelical churches at least, the sermon's supposed to be the high point of worship. Ministers train for years to be able to do it well. So how come so many of us are really terrible at it, and what are the pitfalls to look out for?

1. Verbal tics

Those little habits of phrasing or pacing can irritate the mildest-mannered congregation. That "The Lord is here..." followed by a pause that's so long that people start looking around for him. Or the "Grab a seat" addressed to a staid and elderly congregation used to a little more formality. Spurgeon used to get letters from someone critiquing his sermon, which he used to value enormously. He was fond of quoting the hymn saying, "Nothing in my hand I bring, simply to thy cross I cling". "We are sufficiently informed," wrote his mentor, "of the vacuity of your hands."

2. Over-preparation

One of my lecturers casually remarked once that he always set aside Friday afternoons to prepare his sermons. Plural. We thought he was a hero; we were all at the stage where it took us all week to do one. But the trouble with reading endless textbooks and commentaries is that preachers drown in detail. There's no golden rule about how long it should take, but in the end it has to come from the heart, not just the head. For the sake of argument, let's say that eight hours is too long.

3. Under-preparation

Otherwise known as winging it. A friend was in training and was persuaded by fellow-students of a charismatic persuasion that preparing sermons was unspiritual: he should just pray, they said, and the Spirit would give him the words to say. Let's just say the Spirit didn't, and it was a total disaster. If anything is 99 per cent perspiration and one per cent inspiration, sermons are: don't think God will let you get away with not doing the work.

4. Over-sharing

Families are not given to us as sermon illustrations. The small doings of our children or the attractiveness of our wives or husbands are personal, and not everyone shares our enthusiasms. So talking about a "smokin' hot wife", for instance ­– probably too much information. If you want to talk about something in your family's life, ask them first. On the other hand, you're a human being: don't come over as a walking text-book.

5. Going on too long

But how long is too long? I grew up with sermons that regularly ran for an hour, and if a visiting preacher only managed half an hour there was a strong sense of congregational disapproval. They'd call it spiritual abuse, now, but we thought it was normal. But here's the point: partly it's about what the congregation's used to, and partly it's about the preacher. Long sermons can be fine, but only if the preacher can hold people's attention. That's partly about whether they have something to say, and partly about how they say it: and if they can't do it, they should be told – lovingly, of course, but very firmly.

6. Not preaching for long enough

Not usually a problem, frankly.

7. Being tied to notes

Nothing puts a congregation off like a preacher who won't look them in the eye. Lots of preachers have full scripts in the pulpit because that's how they organise their thoughts, but that doesn't mean they have to stick rigidly to them – and they certainly shouldn't read them word for word. The congregation's relationship is with the preacher, not with a text. If it's obvious that the sermon's just being read, they might as well just get a photocopy to take home.

8. Using bad PowerPoints

Of course they're sometimes useful, to show a picture or a diagram. But using them as headlines and sub-headlines, not so much. Cardinal Newman, who was made a saint a couple of years ago by the Catholic Church, took as his personal motto, "Cor ad cor loquitur" – heart speaks to heart. There's a difference between preaching and teaching, and if we use teaching methods to preach with, we're selling preaching short.

9. Going on a bear hunt

Or a prophet, or a parable, or an obscure theological argument, or whatever. Some preachers are fond of sending their congregations hunting through the Bible for different references, often without even giving page numbers for the pew Bibles. "Now, just keep your finger in Leviticus 13, your thumb in Revelation 5 and turn to Psalm 22..." or not. What are you actually trying to do? Just tell us what it says.

10. Using cheesy object lessons

I know of churches where the minister genuinely believes that a mature, adult congregation will be brought closer to God by the introduction of a puppet during the sermon. Other congregations groan when they see the minister entering the pulpit with a plastic bag in which they know there's some object with a vague relationship to the theme of the address. Perhaps I'm wrong, but I struggle with this. I'd love those preachers to have the confidence to preach the gospel and leave the gimmicks at home.

The best friend a preacher can ever have is someone who won't be afraid to tell them the truth about what they're doing wrong. Yes, it may sting, but you'll be the better for it.