This will be just a quick guide for all backpackers that are going to travel to Kosovo before Serbia, like myself. I will conclude all the information, you can find online, with my very recent experience on the issue (April 2017).
First, and most important, thing is that of course you can travel to Kosovo before heading to Serbia. However you can not go directly from Kosovo. You have to do it via other country that is recognized by Serbian authorities. I, for example, from Pristina took a direct bus to Skopje in Macedonia (just 2h of journey). They ran very often from the main bus terminal, almost every hour. Mine was at 8.30 am. From Skopje you will catch another direct bus to Nis or Belgrade or other city in Serbia. My departure to Nis was at 13.10 from the same station.
Ok, so this all seems not so complicated and easy, but there are loads of issues about not being allowed to Serbia with the Kosovo stamp in your passport. Official uk.gov page adds a real drama to it, as it is written there that you can not cross the border, once you got stamped. Well, how can you not believe the official UK government info? No you can’t. I guess its been written to warn travelers that having a stamp might cause some problems, but it really doesn’t in practice. I’ve had a 2 big, fat Kosovo stamps in my passport and I crossed the border with no drama. Just make sure to ask Macedonian side (or wherever you’re coming from) to stamp you, as they don’t always do so. Serbian border control went through all my stamps with no issues and just put a new Serbian visa in.
I have read that these two governments came to an agreement not to cause any further problem to the travelers, as it`s been known that some were refused to get in in the past. With my confidence, as of April 2017, I can assure you that you can enter Serbia with stamps from Kosovo, but you need to be stamp after in the country you are going via! Much love and good luck xx.