Do:

Acquire country specific suffixes
For example, if you are targeting a Spanish market you should acquire a domain ending with '.es' and make sure it is hosted on a Spanish server.

Use the right language
Use local languages & localised content. It is vital to know what language(s) are used in the country you are targeting. Get advice from a language services specialist if you are not sure. Equally, it is important to recognise the differences within the same language (e.g. English & American English, Latin American Spanish etc). Additionally, it may seem obvious but provide locally specific content e.g. customers in Denmark may not fully appreciate references to Coronation Street.

Design for globalisation
Design your website with potential future global requirements in mind; otherwise be prepared to redesign from scratch at a later date.

Make navigation simple
All visitors are confused with complex navigation. Ensure issues of clarity and usability remain the same.

Promote at a local level
As well as indexing with international search engines, it is also important to index in local, smaller directories and search engines for each target market.

Accept different payment methods
Much of the world does not use credit cards, so cater for alternative methods of payment.

Concentrate on fulfilment
A comprehensive on-line help facility is mandatory & quality control becomes paramount

Don't: 
 
Dive in
It is important to do your research, decide on the most appropriate foreign markets and design a strategy. This will improve your chances of success.

Do it alone
There are many companies that provide business globalisation solutions. Their experiences will save time, effort and will improve the chances of success.

Overstretch your resources
It is better to concentrate your web activity to a few targeted countries than try & bridge the whole world & fail to fulfil.

Ignore international inquiries
It is likely that you will get emails in a foreign language. You will need to have these relayed through a translation agency. Do not ask them to respond in English.

Do it on the cheap
Don't use a friend or relative to do translations unless they are properly qualified. Translation is a linguistic skill that, if done well at the outset, could save you from embarrassment later down the line.