WRONG: If anyone is planning to travel to a foreign country, they had better start preparing early. [" Anyone" is singular. For example, we would never use a plural verb with it: If anyone are going...) " They" is plural. For consistency, if we start with a singular word, we should stay with the singular.]
CORRECTED: Anyone planning to travel to a foreign country needs to make preparations early.
CORRECTED: If anyone is planning to travel to a foreign country, he or she needs to make preparations early.
CORRECTED: If people are travelling to a foreign country, they need to start planning early.
Having said this, we need to recognize that language changes, and this is one rule that is changing (despite all the red ink I have poured over it through the years).