DearLeePing,

　　IhavereceivednoticesayingthatyouwillbeleavingfortheUnitedStatesintheupcomingstudentexchangeprogram.WhileIcongratulateyouonthiswonderfulmission,Ifeelthenecessitytowarnyouaboutacommonproblemforusforeigners.

　　Whenyouarethere,youmightencounterthechallengeofbeingunfamiliarwiththeroadsandthelocationsoftheUnitedStates.Speakingdifferentlanguages,youmightfinditverydifficulttoaskforinstructions,too.Ithinkitisbestthatfirstly,youbringamapwithyouonyourtrip,andsecondly,youshouldlearnthebasicquestionsyoumightendupusinginEnglish,suchas“CanyoupleasetellmehowIcouldreachthisplace?”soyouwouldnotgetlost.

　　Iwishyouallthebest.

　　Yourssincerely,

　　LeeWah

　　(141words)

　　字数可能多了点.我不知道你是不是要用书信形式去写,但既然是给另一个人说的话,我就这样写了,你看看行不行.