The mechanics are simpler than the selling. This is the order that works, and the mistakes that waste an afternoon.

Before you start

Know two things:

Which position you are selling. Below the header and mid-content are the strongest. Sidebars are weak on mobile, which is most of your traffic.

What size. 300×250 if you offer one. Add 728×90 plus 320×50 if you have a leaderboard position.

The order

1. Add the tag to your site. One script in <head>, once, site-wide. This is the only code that ever goes in, no matter how many slots you end up running.

Put it in a child theme or a header-scripts plugin on WordPress, theme.liquid on Shopify, or the custom-code panel on Wix, Squarespace, Webflow and Ghost.

2. Create the placement. Name it something you will recognise in six months — "Below header" beats "Slot 1" — and set the size.

3. Put the slot on the page. Either a <div data-ad="your-slug"></div> where you want it, or a CSS selector so the ad server injects it for you. The second is better if you would rather not edit templates.

4. Load the page. Nothing will appear yet, and that is correct — you have not booked anything. What you are checking is that the request happens at all.

5. Add a house ad. Before any sponsor exists, put your own newsletter or product in the slot. Now you can see it working, and the space earns something from day one.

6. Then sell it. With a live slot and a week of impression data, you can quote a real number instead of an estimate.

The mistakes that cost an afternoon

Selling before measuring. Quoting "about 20,000 impressions" from pageview guesswork, then discovering the slot delivers 12,000 because of ad blocking and viewability. Run the slot for a week first.

Forgetting to reserve the space. An ad arriving and shoving content down is the most irritating thing advertising does. Give the slot fixed dimensions in CSS before anything loads into it.

Lazy loading the top slot. Below-the-fold slots should load lazily. The one visible immediately should not, or you get a visible gap and a slower page.

Using a generated class as a selector. If you place slots by CSS selector, target an id or a semantic element. Hashed class names change when the theme rebuilds and the placement silently stops appearing.

No label. Put "Sponsored" or "Advertisement" on the slot from the start. It belongs on the placement, not the creative, so it shows whichever advertiser is running.

What to check on day two

Then leave it alone for a week

Resist rearranging. You need a baseline: impressions per day, viewability, and the click rate your house ad achieves. Those three numbers are what you will quote to your first sponsor, and they are worth more than any adjective you could write about your audience.