This is some general presentation advice aimed at skilled individuals looking to offer their services. While this was inspired by some particularly bad advertisements in the visual novel community, the advice is broadly applicable.
Present yourself confidently, but modestly. Don’t say “I think I’m a pretty good artist” or “I’m not very good but …” — the former sounds narcissistic and the latter makes it sound like you have no faith in your abilities. Instead list what you can do without qualifying it. Omit things you’re not confident about.
Get your work in people’s face as soon as possible. Nobody cares about your life story before they know you. Put the art, audio, writing, code, diagrams, or whatever else at the start of your advertisement.
Keep things short. If you’re a writer they’ve decided after the first paragraph or two whether or not they want you. If you’re a musician, the first two tracks. An artist, the first two images. And so on. Link to longer content for those interested.
Show off only your best work. It’s better to show one good thing than a good thing plus a not-so-good thing. Your weakest example is your strongest so exercise restraint.
Format your post for legibility then aesthetics. Use desaturated dark text on a light background (or light text on dark background) and left-align paragraphs. No exceptions. Keep things short and break information into logical chunks with headings. Use lists for information people will want to quickly scan such as pricing lists. Proofread your post before submitting it.
Assume that people will search the profiles associated with your name or handle. This includes anything you link to. If someone ends up on your Deviant Art profile and sees a blog post where you describe yourself as “lazy” they’re not going to contact you.
Personality is fine as long as it doesn’t contradict these points. There’s nothing wrong with some nice formatting or mentioning your interests, just make sure the formatting isn’t actually aggravating or your interests long-winded and/or unrelated.
List information, don’t make people ask for it. “PM me for details” — No. You post the details or I close the browser tab.
This is advice not law, nor complete. These are personal rules of thumb and I bend or break them occasionally.