Design - Go for simple classic designs. Have a look at other sites and see what works. Most sites have one two or three columns and this is the best way to go. One of the best websites out there is the BBC news website which just has two columns. But look at the use of headings and boxes that attract the eye. Lay off flashy websites which have moving graphics and text. What you might think of as cute and funny could put other people off. Keep colours to a minimum and fonts and text size consistent throughout the site.
Search Engines - Search engines need to be able to know what your site is about. Make sure you have unique meta titles for each and every page. Use headings with the most important words in them. Forget having a heading with the usual waffle of welcome to our website blah blah...'. If your website is about Women's shoes' make sure the heading and title of the page uses the words Womens shoes'. It sounds simple enough but so many websites make the mistake of calling every page their business name. This is fine if your Tesco or Virgin as they are big brands, but for smaller business that are not well known you need to find your customers. Keyword research is very important and Google have a useful tool to help. Just put into Google Google keyword tool' and it will show up top. Once you have chosen your keywords, add them to your site. Don't overdo it, just a couple occurrences' of the words will do. Just make sure the titles and headings have these words in them.
Navigation - Finding your way around a website is all about having a good navigation structure. This is also important for search engines not just real visitors to your site. Have plenty of internal links and where possible use keywords in the anchor text. Many websites use the words click here' as the hyperlink but this is telling a search engine nothing. If you use keywords in the hyperlink you are telling a search engine that that page is about something.
Getting your message across - Make sure you are getting your message across. If your business offers the best resource for say pet care, make sure it tells and shows visitors that. Don't talk the talk if you can't walk the walk. Also don't hide anything away. Everything your site offers should be just one or two clicks away. If finding things is hard on your site you may as well just bin it and start again.
Be the best This is probably the best and most obvious tip. There are millions of other websites out there so for yours to do well it needs to simple be the best in its industry. What are you competitors' NOT doing? What are your competitors NOT offering? How can we be the best? These are questions you should be asking yourself and them implementing.