Look for an appropriate and reputable travel agent, and discuss your journey plan thoroughly, in order to chalk out all the details.
A few well known travel advisers are:
A1 Travel Services
Abbotts Travel Agency
Thai Airways International
Waterstone's Booksellers Ltd
Follow the instructions given by the agent and make sure you take along all the items the agent advises you to. Travel agents are well aware of all the scenarios that can arise, so take their advice seriously.
Keep a map and a route plan with you, which has detailed directions – this will prevent you from getting confused during your journey, and enable you to make sure you are on the right track.