If you are on an IOS device (I'm on my iPhone) you can click on your playlist and scroll all the way up to where you see a bar that says "Filter". If you look to the far right there will be a icon with 3 little bars. You can click on that and change how the songs are sorted and if you click Recently Added then it will make all the newest songs added to your playlist at the top. Hope this helped!
Most of my playlists are quite long, and this process is VERY time consuming. I share my spotify playlists with wedding clients, and have many playlists for different times in the evening. I prefer for the most recently added to be at the top, so i dont come accross as a dj that is playing 'old' music. And the good new exciting fresh stuff gets missed at the bottom of a huge playlist!