First you have to be noticed
In making an ad, priority Number 1 is getting your audience's attention. Generating enough impact to cut through the clutter. The average person sees or hears hundreds of advertising messages a day. From cereal boxes to the backs of buses. Newspapers and billboards. Radio and TV. To cope, target audiences have evolved an amazing ability to ignore just about all of it.
   The clutter is even worse online. As of 22 January 2022, WorldWideWebSize.com reported that the indexed web contained at least 2.39 billion pages. (That looks like this: 2,390,000,000.) And each and every one is available to people using the Internet. At the same time, these users have become the most fickle of audiences, empowered by their mice to reject anything that even suggests it could be a waste of their time. Needless to say, making a website that confuses them, or annoys them or looks like everyone else's is not the way to go.

Tell them how they benefit
Once an ad succeeds in getting someone's attention, it must hold their interest long enough to get the message across. The same goes online. As easy as it is to flip a page or flick a remote button, it's just as simple to click off to another site.
   It stands to reason that the best way to keep someone interested is to tell them something they want to hear. Something relevant. Something that will improve their lives or how they feel about themselves. In short, a website, just like an ad, should tell users what's in it for them.
   Of course, you can't do this until you know who your audience is. And where they're coming from. The more you know, the more accurately you can aim your message. And the more likely it is to connect with the people you most want to talk with.

Make them an offer they can't refuse
Once you stop people and manage to hold them long enough to deliver your message, the next step is convincing them to actually take some action. In other words, compelling them to buy whatever you're selling.
   Obviously, this third point doesn't have a whole lot of relevance if your site is just there to provide information. But if you are selling something - and that includes yourself - you have to be at least more convincing than your competition. As you've probably noticed, very few web developers - or the technical writers they employ - have any experience in this area.
   It's worth pointing out one huge advantage the Web has over all other advertising media: space. A well-conceived website can provide enough 'sell' to convince everyone from the casual tyre kicker to the dedicated knowledge hound. Makes you wonder why so many sites seem to skimp.