Remember, always count your beats before you mix them together. Slam the first beat of “Song A” right on the first beat of “Song B” when the proper timing permits. Use your ear. Also, the EQ’s are the ultimate mixing tool, next comes the sound effects. It is always important to remove the bass on “Song A” before bringing in “Song B”, and as “Song B” begins to rise, lower the bass on “Song A” then bring up the bass on “Song B”. This will provide for a smooth transition.
Though difficult to read and understand, follow these steps with your mixing tool. You’ll find it to help, especially with bass-y songs like dupstep.
Also, don’t forget to make sure they are the same BPM!