Here are a few tips for you (an owner of a website) to have a successful website launch.
You need a plan
Set a launch date, and make sure it is reasonable with your web designer/developer. Check in with them throughout the project to ensure everything is on track. Make sure you are keeping your end of the deal (i.e. making time to review items, give feedback, test things, etc). Keep a list of things that need doing and refer back to it often, so if something needs to be added to this list, make damn sure it’s important and doable within the timeframe.
You need content
Most web design projects don’t include content. So make sure you’ve written (or have had written by a professional) all the words required for every part of the site. This takes more time than you’d think, so budget for double the time you think you’ll need. If your website has a blog, make sure you’ve got at least a couple blog posts in there before launch. This will give visitors a sense of what to expect in the future.
You need social media
Have you setup your twitter account? Facebook page? LinkedIn profile? Ensure all your social media lines up with the new site (colours, logo, design, etc) and that they’re all connected. Feel free to tease your social media followers with the launch date, and get them excited about it and make yourself accountable to the date.
You need third-party services
All sites need some additional services to be as awesome as possible. Services like FeedBurner (for RSS/email subscriptions), Google Analytics for stats/tracking, Disqus for more intelligent commenting and/or a newsletter program to collect and send out emails to your subscribers (like aWeber, MailChimp, Campaign Monitor, etc). CloudFlare is another amazing (and free) service that speeds up your site by doing some DNS and caching magic. These services all need to be tested and working before launching your site.
You need to test everything
You are relying on your web designer/developer to build you a kick-ass site, but it’s also your responsibility to test everything they’ve done. Click every page and link, fill out every form, proofread every sentence, test your RSS feed… do every single task a visitor to your site can or will do to make sure it works correctly. It’s better for you to find bugs before launch than have visitors do your bug-testing for you, publicly.
You need to launch
On launch day (congrats, you made it!) start your promotion engines and get promoting. Tell your friends, family, followers, subscribers, everyone (but don’t be annoying). Offer discounts or freebies, if applicable. Have some ephemeral and/or fun thing going on for the launch. Look at your stats and mentions and personally thank folks who are promoting and talking about your new website.
Everything else that needs doing, your web person can (and should) do for you – setting the DNS, making sure the site is index-able by google/search engines, generating a site map (as a page and as XML), creating a favicon (the little icon beside your URL in the browser), as well as a myriad of other tech details. You are relying on them to do the nerdy bits, so keep up your end of the launch by taking care of all the other above tasks.