When considering a complete overhaul for your website, remember the old acronym: KISS, or Keep It Simple, Stupid. KISS definitely applies to websites. Simple is best, but don't mistake simplistic for a lack of depth. You'll want to make sure that your website offers a full, complete experience for your visitors, but you don't want to overwhelm them with flashy graphics, overly-large banners, or cluttered sidebars. Instead, focus on plenty of white space, grid layouts, clean lines, and similar but distinguishably different fonts (try to stay within the same family; but alternate between serif and sans-serif for headings and paragraphs) for a sleek, sophisticated, updated look. A "visit us today" link, for example, should stand out from surrounding text, but not overly so - a subtle color change and underlined text should suffice.
More than anything, make sure your visitors are able to quickly achieve their goals. This means if they're looking for informative articles, they can quickly find them - either by browsing categories or using search tools. Likewise, for products, use categories as well as tags to carefully organize your merchandise, and make sure that search filters look not just at categories and tags, but any file and image descriptions you use. The more information you add to your site, and the more information you make searchable, better.
Finally, you'll want to complete your updated website by making sure it is search engine friendly. Brush up on your SEO, or hire an internet marketer to help you fine-tune keywords, optimize individual pages, and add the META tags search engine bots are looking for when indexing your website.