When visiting a foreign country, make sure that you check if a visa is required. You can do this by calling your airline/bus company, boat or rail or checking their Web sites under "International travel." Give yourself ample time as sometimes it is necessary to mail your passport to the consulate/embassy in another city or you have to wait a few days after submitting your passport to the consulate/embassy.
You should also ensure that your passport has at least a 6 months validity and a few blank pages so the visa can be placed in it.
Health requirements are very important as some countries may require a vaccination before entry. This is common for countries in Africa and South America.