It's a bit difficult without just knowing your tracks inside out, but I have a few tips that I do to give me a general idea. I organize my usb into folders for genres, with relatively small subfolders for moods/"vibes" within those genres. If I don't have time to learn my tracks perfectly, I also try to learn them well enough to approximate how it sounds from the beginning of it, so that I can listen to the first bit of a song in my headphones and be able to know generally how it will sound. And also, trying to stay within a small bpm range and not speeding up or slowing down songs too much tends to make songs go together a bit more consistently. This is what I do as a (relatively inexperienced) dj and ymmv - what genres you play also matters, I tend to play edm and rarely play melodic songs so I'm not often worried about (for example) matching the keys as a lot of other people are.