There are a large number of Postcrossing members who make handmade cards to swap - here’s a thread that showcases what cards people have made & a whole section about all kinds of issues about handmade cards.
People also often get postcards printed with their own photos as well.
Enjoy!
I can tell you this: find what you prefer to do, collage, drawing, colouring with watercolors or pencils, ink, make photo, draw somethig of your city or country… and use that and your imagination to do your postcards. 
Hello What you want to do is completely up to you! My advice is to use thicker paper similar to normal postcard so that the postcard survives. Some people use cardboard, I glue two drawing papers together. And if you make a collage with something that may fall off, it is a good idea to use an envelope (I used dried leaves once and the receiver said they were gone when she received the postcard). Have fun!
I have read that some members make their own postcards, my question is how exactly do they achieve this task or in other words I would like to learn how to begin making some as well. Any suggestions on how to begin and personal experiences to that you can offer for specific themes, such as from comics to picturesque scenes.
Maybe come and have a look around here: many nice inspiring works as well as many people who might help you and give you tipps
I either do mine as a sort of collage on cardstock, or I have a photo printer that I am hoping blank postcards will print through. I have yet to attempt this yet, as the blank postcards only arrived today. I will keep everyone updated on this. I have also embroidered some cards in the past, but these had to be sent in an envelope.
So far I have started by this, I bought cardboards, used tape to keep them straight when using water colors or opaques. I havent tried anything else yet but I’m interest to get some tips for embroidering - never done that.
Heres me projects
The palindromeday card is really lovely!
When I make handmade cards it is mostly collages on blank notecards. I’d love to start on other cards as well, but feel I lack the creativity.
Best: Take your time to browse the topics in #postcard-mail:mailart-handmade-stationery.
There are even tutorials you can follow:
And there are many topics where various aspects of making cards are being discussed.
Maybe that one might help you?
Bad news on this front. As the postcards I ordered accidentally weren’t glossy fronted they wouldn’t print through the photo printer. I did however attempt gluing photo printer photos onto them, but that didn’t seem extremely stable and would have to probably go in an envelope- which I was trying to avoid.
I have received one of your drawing as official card 
love it!
If you want to print your own postcards, you can take your own photos and edit them using photoshop/ illustrator. Since you’re from China, you can print them from TaoBao shops, just type 定制明信片 and you will come across a tonne of options. They even allow you to design the back of the postcard ^-^
(I haven’t try printing my own cards yet because shipping to Malaysia is expensive, but the reviews seem to be very good for many of these shops)
I think everyone feels lack of the creativity time to time, me too and sometimes nothing works. I hope you keep trying.
Having a few topics preselected by the receiver helps me a lot to spark my creativity! I invite you to https://community.postcrossing.com/t/handmade-postcards-choose-a-subject-tag/6238 . Maybe it will get you inspired too! There is also the Handmade RR if you prefer to make several postcards on the same topic 
@lemontoffy and @hankadl thanks for your kind words. Somehow I feel like my creativity ran dry during the past years. I will check your links and hopefully will start to get going again. I’m just a bit afraid that people won’t be happy with what they receive.
I know. I am always worried too (and actually I have need to gratification other people so much that it´s not normal I guess). I send self made cards only to them who have mentioned in their profile they are willing to get self made cards. Or sure in self made card tags.
I love that you want to make your own postcards. I use [Postcards - No Minimum Quantity | Zazzle] Sometimes I use my own photos for this. I have been super happy with the results and it is a simple process.
Diane
Here is one of mine