You typically focus on what to do during a sales call or presentation, But just as important is learning what not to do, identifying the actions that can instantaneously destroy your chances of making a sale.

Here are five commonsense but often-forgotten don'ts of the sales call. Ignore them only if you want to kill your chances with a customer.

1. Don't be late.

We've all been late at one time or another, but in sales, lack of punctuality is a real problem. In the worst case, being late for any appointment sends distressing signals: that your time is more important than the customer's, that you don't plan well, that you aren't trustworthy. If you have been detained or delayed and the situation is out of your control, always promptly call to apologize and ask for a reschedule. The earlier this call is made, the better. You want your customer to know that you respect their time--if you don't, they won't respect or trust you.

2. Don't dress improperly.

We all grapple with the timeless dilemma : Should you dress very well to show off your success, or should you underdress to give the impression that you need the business? The correct answer changes depending on the industry and situation. However, the safest bet is to dress similar to how the customer dresses, or how you guess they will be dressed based on the industry or office environment they work in. People are more comfortable around those who are like themselves, so do your best to match their level of sartorial formality.

3. Don't do all the talking.

You walk into a sales presentation and you get the urge: Talk, talk, talk, pitch the product, explain what you can do. But your real goal is to give the customer what they want, and you can only figure that out by asking smart questions and listening closely. Studies have shown that customers remember best what they tell us, not what we tell them. Your customers will remember their answers to the right questions long after the presentation was made. So, don't fill up the session with your voice. Let the customer talk and make it your job to find out what they want.

4. Don't bash the competition.

One of the worst things you can do in a sales call is bash the customer's current supplier or one of your competitors. It's always considered poor etiquette, and will almost always repel the customer from you. Especially if you're tempted to criticize a customer's current supplier, remember that they chose that supplier themselves--and no one likes to have their decisions belittled.

5. Don't be overconfident.

Even if you believe the sale is imminent, don't forget that every customer, regardless of your relationship with them, has other suppliers they can choose. Don't take the business for granted. I did this once early in my career, and I ended up losing a big account thanks to my cavalier attitude. That was a hard lesson learned, and a mistake I won't make again.

There they are: the five big don'ts of the sales call. Steer clear of them, and you'll set yourself up for sales success!