Step one: Be Picky
Obviously choose your best work, but don't assume you know which pieces those are. Ask your people you know what appeals to them most and take that into consideration. Aim for 15 pieces that represent work you want to keep doing.
Step two: Don't Reinvent the Wheel
Don't be afraid to use a portfolio template site. I made my own site and hosted it for nearly a decade, and after getting hacked several times I'm over it. Now I'm on Squarespace because it's easy to manage and stylish. Plus, if something goes wrong, I'm not on my own. They have AMAZING customer service.
Step three: Big Images, Small Type
Images should be at least 500px wide. If possible, take photos of your work in context: photos give your work presence and warmth and context shows your work's personality.
Keep your type small and classic. Use a nice, legible font with a bit of personality. As a general guide, choose sans-serif for headings and serif for descriptions. Don't try to wow with your typography skills since your images should be most important anyway.
Step four: Describe your Work
SEO (being found by a search engine - "search engine optimization") is a big consideration for your portfolio since that's how you can get new clients, customers, and fans. I've been told by the experts that writing meaningful descriptive headings (with proper html tags like H1 for the title, H2 for the sub-heading, P for paragraph, etc. ) and explanations of your work using key words (words that you want to target specifically, ex: modern, bold, illustration, etc.) is the best way to be found.