Instructions for Form W-8BEN
Hands down the best set of instructions to follow are those on the Internal Revenue Service web site. These instructions for form W-8BEN are fully comprehensive.
The Univertsity of Washington W-8BEN instructions are a handy summary to take a look at too.
But remember you also have the flexibility to create your own form, as the IRS notes, ‘You may develop and use your own Forms W-8BEN, W-8ECI, W-8EXP, or W-8IMY (a substitute form) if its content is substantially similar to the IRS’s official Forms W-8BEN, W-8ECI, W-8EXP, or W-8IMY (to the extent required by these instructions) and it satisfies certain certification requirements.’
The IRS adds, ‘You may develop and use a substitute form that is in a foreign language, provided that the substitute form also provides the English version of the statements and information otherwise required to be included on the substitute form. You may combine Forms W-8BEN, W-8ECI, W-8EXP, and W-8IMY into a single substitute form.’