obtain a visa on arrival at the customs in Vietnam. You need to bring an invitation letter, which can be applied for online: Vietnam Visa online (takes 2 days). Make sure you take U.S. Dollars and 2 passport photos with you.
go to the Vietnamese Ambassy in your country. Usually they need 2 passport photos
Not more than 30 days: for citizens of Asian Nationals such as Indonesia, Laos, Malaysia, Philippines, Singapore and Thailand (except Myanmar & Cambodia).
Not more than 15 days: for citizens of Denmark, Finland, Norway, Sweden, Japan, South Korea and Russia. French citizens holding valid diplomatic passports are exempt from visa requirements and are allowed to stay for up three (03) months at one time or on several visits within six (06) months since their first immigration dates.
Citizens of Chile holding valid diplomatic or official passports are exempted from entry transit visas and are allowed to stay for up 60 days on each visit.
Starting 1 July 2015, citizens from the United Kingdom, Germany, France, Italy and Spain will be allowed to visit Vietnam visa-free for 15-day stays. The initiative will be valid for two years.
Recently the E-Visa was introduced, which makes is even easier. See here for more information and application. In that case you don't need the 'invitation letter' any more, because you already have a visa.