You can go down to a Vietnam embassy and grab a full visa but if your not near one or dont have the time the best bet is to buy a letter of approval online and then use that to get a visa when you arrive, here how.
First apply and pay for a letter of approval, I found the cheapest one to be from https://vietnamvisa.org applied and paid and had my letter back in a couple of days. I chose the cheaper option of having a multiple name approval letter, it makes no difference it just means there’s a load of other peoples name on your approval letter as well!
You need to take with you:
-Passport (Durh!)-Approval letter
-Passport photo x2
-USD$ to pay for the visa (Single entry is $45)
Print this visa form and fill it out on the plane if you want to save time when you arrive and get you visa issued first.
(Click the image for a full sized version)
When you arrive follow signs for ‘visa on arrival’
To save time and get in the que early, print this form and fill it out before you arrive. Go straight to the desk, hand in your visa approval form, one passport photo, the entry stamp form and your passport.
Head down the short corridor on your right, wait near the window for your name to be called (they have a screen with the announcement if you can’t get close enough to hear) and receive your passport back and pay the fee.
Make sure you have USD cash to pay the fee and make sure you have extra in case, as they rejected my $50 not for no reason and wouldn’t let me pay with it!