Before I mix a tune I listen in the headphones to see if it is in a key that will go with the tune that is playing. I try not to cut the bass entirely when bringing the tune in but have it at say the 8 o'clock point, depending on how long the mix is I bring one channel up and the other down slightly so that the tune I am mixing in is becoming more dominant but the bassline is not there yet, then at a point normally after a drum roll or whenever I feel like it really I wack the bass in! Then realise I havn't been listening to the headphones for 2 minutes, the tune train-tracks, I throw my headphones on the floor and stomp out the room leaving the two bastard tunes to fight over each other. Ignore the last part its not true I'm actually a proffesional