First start with dear friend:
                                         hi! you are fine my friend. as you will remember by birthday. it is right on 13-2-2016 there is a party organised in my home , so, you must come with your family.i will  be waiting for you. i will send  my address in massage. as soon as you come to India, call me, bye i will be waiting for you.
                                                                                             your lovely,

Dear friends name,
Hi, how are you I hope you are fine. I hope this letter
will find you in the best of your health.
You will be pleased to know that my birthday is coming.My birthday will be celebrated on 18th Dec IN Kolkata.So I request top reach here on our before 18th Dec.I will be waiting for your arrival.
Your caring,
Your name