Here are some general pointers:

1.Grammar: Make sure you use correct grammar and syntax. It is important for visitors to understand what you're trying to say, so keep your sentences short and beware of typos, which can make you look unprofessional.

2.Readability: Carefully select your colour scheme. It should definitely mirror the client's logo, but it should also be readable; No one is going to read your text if they have to squint. So keep your background light and your font colour dark, while adding accents of colour in headers and/or links. Also, the font size of your main text should be large enough for people to be able to read in different resolutions. However, if it is too large it would look cheap and childish so experiment and find a 'golden ratio'.

3.Loading Times: Nowadays, page loading time is shorter than it's ever been so try to avoid anything that will cause delays. This includes pictures and Flash objects. However, that's not to say that they should not be used at all. They keep your website interesting and more polished.

4.Be concise: Keep all relevant information for a topic to a single page. People sometimes fail to notice the "Next Page" link or they simply haven't got the time for it. It has been observed that people on the Internet merely scan texts instead of reading properly, so try to keep details to a minimum. No one likes to scroll down for ages in order to find what they are looking for.

5.Technical Terms: Care should be taken to identify your target audience. If you expect your website to be read by non-experts, make sure you explain any jargon and acronyms carefully. What is common sense to you might not be to your visitors.

6.Advertising: As far as advertising goes, it is a necessary evil. You should not, however, allow adverts to break up your text or take centre stage, such as pop-up windows. They are likely to confuse visitors as well as damage your website's credibility.

7.Be consistent: There should be a common theme throughout your website, including colours, page layout and font. This keeps your website looking professional and easy to navigate.

8.Maintenance: Frequently check all of your links to make sure they still work after things have been added to your website, or after a re-launch. Take extra care with links to external websites. There's nothing worse than a list full of 'dead' links.

Conclusion

Last but not least, don't forget to think like a visitor. Have your friends and family visit your website before the official launch; as outsiders, they might spot something you haven't, and their feedback is the most useful.