Lots of great advice here. Love watching DJ's help each other out instead of trashing each others technique lol. Reading the OP's post, makes me remember when I first started mixing. Drum and bass is basically all I've ever mixed. Prior to DJ'ing I just listened to the music, never really understanding the "roadmap" of an dnb song. When I started DJ'ing I'd get lost in the songs pretty easily, mainly because I didn't know my records as well as I should have and I didn't understand the mechanics. I was taught the mechanics one morning at an afterparty by another DJ; practiced every day for hours after that until I nailed it.
The beauty of mixing today, if you're on a controller, is you don't have to worry so much about hardware. Back when I started DJ'ing I remember, you had to have technics 1200's or you were just going to struggle. As everyone has stated here, figure out the intro's, outro's and phrases and you'll be golden. And for awhile, you'll be listening to every track and counting "1-2-3-4, 2-2-3-4" lol.
As far as that perfect mix... man, thats hard as hell to come by when you know your music REALLY well. The perfect blend between 2 songs is all you'll really hear. Beyond that, you'll hear everytime those beats go off, even by 1/32nd *sigh* That used to piss me off, but its the nature of being the guy behind the decks doing the entertaining.
EQing is crucial to getting that flawless mix. Practice that after you have phrasing down.
I remember when I got phrasing down with my turntables. Was a great day lol! Shortly after that, I got a mixer that had decent EQ's for hi's mids and lows, and kills switches for all three.
When I blend tracks, I really only look for a similar "feel" between the tracks. I'm not going to go from a light song to a hard drop. My mixes consist of hard and lighter tracks so when I transition, I usually use bassless portions to go from hard to light tracks (or acapella intros), and from a light track to a hard track I use a build up swap. All I can really say is just play it by ear. If you transition and you yourself feel that the songs don't really change off too well, it's likely the crowd will feel the same. This is also a technique heavily based on the genre you're mixing.
I recommend learning what each control/knob/function does on you're mixer/controller etc. Then watch how the big DJ's use these to complete good transitions.
Boiler Rooms with overhead cameras on the decks are great for this.