Check that your passport is valid and covers the dates of your trip for the countries you will be going to. Many countries will give a 30 day or longer visa at the airport on arrival for British and European citizens. If a visa is required, you will have to visit the Embassy or Consulate for that particular country. A list of Embassies and Consulates is available at the
Foreign & Commonwealth website.
To avoid delays with regards to obtaining a visa, always answer all relevant questions on the visa application form and bring along all necessary documentation and proof of identity as stated on the the Embassy's website.