As I mentioned before that it’s very important to get your tone right in General Training IELTS Writing Task 1. Here are some good greetings and salutations in an informal letter.
Friends usually have names ;-) so address him/her with a name: begin the letter with Dear Joey/ Tim /Rebecca, etc.
Begin your letter with some general statements. Refer to the letter you have received from your friend and thank him/her for it or apologies for the fact that you have not answered the last letter soon enough.
Use the proper register. The letter is supposed to be informal so you can use contractions, informal linking words like well, by the way, anyway, so, colloquial expressions, etc.
You can use more-conversation-like statements or questions in your letter: You know that I had this exam, right? You think he will be able to come to the party?
Use questions to ask about your friend – arrange the next meeting, send greetings to his/her friends and family, etc.
End your letter in informal way: Best wishes; Love; Regards.
Dear + first name, (E.g. Dear Jeffrey,)
I hope you’re well.
Hope all’s well.
Thank you for your letter. It was nice to hear from you.
I'm sorry I haven't written for so long but…
Hope to see you soon,
Love from yours,
Your first name/nick name (E.g. Tom/Amy)