For your journey to be trouble-free you´ll need to make sure your passport´s in-date and in good condition. You´ll also need to have the right visas and documentation for all the countries you plan to visit before you go. If you don´t have the right paper work on arrival in a country, you won´t be let in!
Here´s a checklist of things to check before you go:

• Check the expiry date on your passport before you travel. Your passport needs to be valid for at least six months from the date of your return. If you turn up at check-in with an out of date passport, you won´t be allowed to travel.
• Check visa requirements with your travel agent or the relevant Consulate or Embassy of the country you plan to visit
• Make sure that the details of your next of kin at the back of the passport are up-to-date.
• Apply for your passport in good time. Once you´ve applied allow at least four weeks for it to be ready. To be on the safe side do not make any travel arrangements until you have your new passport. In the UK, advice on how to obtain a passport is available online at www.passport.gov.uk or by calling the Passport Adviceline on 0870 521 0410.
• Outside the UK, you should seek advice from the nearest British Consulate. If your passport is lost or stolen overseas, contact the nearest British Consulate or Embassy immediately.
• Take photocopies of your passport data pages and keep one copy with you in a safe place whilst travelling and leave one copy with family at home. Lock your passport in the hotel safe and carry your photocopy with you. Consider holding your passport details in a secure e-mail account, so should you lose it, you can access the information quickly.
• Make sure you have enough blank pages for entry stamps: some countries demand a completely empty page for their entry stamps and if you are visiting several countries in one trip, as is often the case with gap travel, you can be caught out.
• If you´re visiting the USA under the Visa Waiver Programme, you should ensure that you have a machine readable passport.
• Ensure your passport is in a good condition - if your photo has been damaged or any pages torn or removed, you will need to get a replacement one.
• Take a second form of photo identification with you.

Source: www.gogapyear.com