By its very nature the world wide web and the websites that make it up are ever-changing, with new design mechanisms and ideas appearing frequently. This means that your web design can quickly start to look 'old' and out of date.
So what can you do about that? Well, not much really, other than making certain that your design and construct are up to date at the start and that the design matches your idea and your business. Never be afraid to update your site if you feel that the design is no longer working for you, but remember that you should at least try to keep to your basic design for continuity reasons.
When you are starting out with the design process it does no harm to check out other websites of businesses similar to yours for ideas. Approach your web-designer and discuss your ideas. Remember, two heads are better than one! Put your page layout down on paper, so you can see what it may look like. Play with ideas, and don't be afraid to experiment - remember that websites today are very different in structure from what they were even a few years ago, and mainly because of experimental design ideas!
Think carefully about things like colour combinations, fonts and font sizes, icons and graphic images. Try not to put too much on one page, it must be easy to navigate and read. Put as much valid content into your site as you can, because content is king! Search engines are in the business of providing relevant content to searchers, and if your site is relevant, up-to-date, and has plenty of quality content, you are halfway to getting a good page rank!
Try to avoid too much 'gimmicky' content - flashy images, rollover content, mouse-over changes and so on - your site should be clear, concise and easy to navigate. Avoid garish colours wherever possible, and avoid using sound unless there is a really good reason for it. Make certain that your navigational system is intuitive and attractive. It it is easy for a human, it will be easy for the search-engines too!