During my highschool period I had quite a lot of penpals.
Back then I had enough time to send many emails and read all the replies. In some cases we exchanged just one or 2 emails and then the communication stopped.
Nowadays I don write with penpals anymore, but it was definitely a great experience! I'll mention a few reasons why you might want to write with penpals: Getting started is really easy.
(You can find a list of some penpal websites on the bottom of this webpage.) On many websites you also have the possibility to make a profile of yourself and post that on the website. But if you're lucky ,it might also result in a very good friendship.
Just be careful with the amount of information you post on your profile, but paranoia probably prevents a interesting conversation.
Building a solid email/snail mail friendship is quite hard.
In the first couple of messages you probably exchange name, age, what you do in daily life , hobbies and sports . If you're lucky you have one or 2 things in common, for example a hobby or you are both fan of the same actor or artist.
Then you can discuss the ins and outs on this subject.
After that you have to find some new subject to talk about.
A suggestion is to tell about those simple things you experience in daily life.
It might sound like very normal to you, but can be very strange/exciting/funny to somebody on the other side of the world.
Another suggestion is to exchange some words/sentences in your own language with your penpal.