Don't put "Under Construction" signs on your site - it makes you look like a total amateur (OK, so you are an amateur, but you don't have to look like one). A website by it's very nature is always under construction. If it's so under construction that it doesn't work, why did you post it on the net?
Do include a few images, and maybe the odd change of text colour for emphasis. In other words, "decorate" it. If the site looks attractive, visitors are more likely to read what you have to say. But....
Don't get too carried away with text colours or font changes. Two or three different colours or fonts (typefaces) look good (but remember that font changes often have no effect on webpages). Any more than that just looks messy. The same principle applies to images.
Do put a link back to your index page on every page. Don't just rely on the browser's "Back" button to get visitors back to the index, because someone who found your site on a search engine might not arrive where you expect - if they start on a sub-page which has no link to your index page, they'll never see the rest of your site.
Don't bet the whole site on one technology. If the site only works if people have java enabled, or the latest Flash plugin, people who don't won't be impressed. And don't try to make the relevant plugin load automatically if a visitor doesn't have it. It just annoys people. They won't wait, they'll just cancel the download, curse you, and leave, never to return. That doesn't mean that you shouldn't use Flash or java, or put in a link to let visitors download the plugin if they want to, just make sure there is a working alternative for people who don't.
Do keep your paragraphs short. People tend to skip over big paragraphs rather than read them properly. For the same reason, put the most important bit at the beginning of a paragraph rather than the end.
Don't make your images too big. It doesn't matter how pretty it is, if it takes ages to download most visitors will get bored and leave without seeing it.
Do spellcheck and proofread it carefully. A website that is littered with typing mistakes looks awful and puts people off very quickly. And check it thoroughly online as soon as you have uploaded it - visit every page, make sure every graphic displays properly, test every link. Get a few friends to look it over before you start publicising it, too. It might look fine in your browser but horrible in everyone else's.
Don't submit it to search engines before it's ready. A lot of search engines take a snapshot of your site when you submit it. If half the links don't work because you haven't written the pages they link to, or you haven't sorted out your meta tags yet, your listing will look terrible, if you get one at all, and anyone visiting isn't likely to come back.
Do swap links with similar sites. Sites that have lots of links leading to them get a higher ranking in many search engines.
Don't put words in your meta keywords tag that have nothing to do with your site (see Search engines and meta tags) , in hope of getting found by more searches. It is more likely to get you put to the bottom of the list than the top, as the search engines are wise to it. And anyway, people who get directed to your site under false pretences aren't likely to be too impressed - would you be?
Do keep your style consistent. By all means create different websites in different syles, but within one site stick to one style for things like background, text style, where you put links and what they look like and so on. If the look is totally different on each page it just looks messy and confuses people.
Don't use pop-up consoles. (You may have noticed that I haven't told you how). A lot of people hate them and close them the second they open without ever seeing the content, or even disable them completely, because on nearly all sites that use them they only contain advertising.
Do look at other people's source code. It's absolutely the best way to learn. Don't worry if you don't understand all of it, you'll pick it up as you go along, and it's usually not too hard to find the part that is doing whatever it was that impressed you.
Don't use HTML frames unless you are absolutely sure you know what you are doing. And even then don't if you can avoid it. Some browsers don't support frames, and also a lot of people hate them and always browse with that feature turned off. Worse, most search engines can't index them properly without a lot of messing about on your part. If frames are done well they can be effective, but all too often they are done badly and just annoy people. And for most purposes you can get a similar effect much more simply and reliably by using a table.
Do add the Width, Height and Alt attributes to every image. It's a bit of a pain, but it helps to make a good first impression (you never get a second chance to make a first impression) and generally makes your site more user-friendly.
Don't spam newsgroups or via email. You will see all kinds of adverts for lists of millions of email addresses that you can buy, to send publicity to; and scams that encourage you to post messages to multiple newsgroups, regardless of what they are about. Don't do it. This is called spamming, and is the quickest way to get your account cancelled and your website taken offline. Internet users absolutely hate it and will certainly complain to your ISP, and almost all Internet Service Providers will react to such complaints immediately, by chucking you off their network. Permanently. If you think I'm exaggerating, go to your ISP's website and look for their Acceptable Use Policy (AUP) document.
And most important of all :
Do... enjoy it!