Find all the sounds that will be used in your Schranz song. Schranz sounds are dark, gritty and often come from classic analogue synths such as the Access Virus. Virtual synths might emulate these sounds well if a hardware synth is not available. Create the main musical motif once all the sounds are assembled.
Tweak your sounds as needed. Loops, samples and percussion kits are often compressed and filtered. Percussion sounds are also lo-fi to heighten the grittiness of the tone. Bass drum hits should have an exaggerated bass tone.
Create a structure for the song. Schranz is not overly complex in terms of musicality. Simple pads and sweeps are a good portion of Schranz.