I've had dermographic skin condition since I was 5 y/o. I'm now 25.
I would say limit your acidic foods and drinks intake (citrus fruits, coffee, alcohol, etc.) - it will help subside the symptoms.
I also noticed that natural tanning (laying out and tanning on the beach, not indoor tanning) has helped 'neutralize' my skin so that it is less sensitive and does not get as red/does not get bumpy as much when I have a tan. I have heard of this before too and, contradictory to what some dermatologists might tell you, I believe it actually does make the symptoms appear less frequently.
Also, I would suggest trying acupuncture and Chinese medicine to help calm your nervous system (as this condition is related to your nervous system balance). Acupuncture works wonders! I've used it for reducing stress and anxiety, for curing digestive issues and IC.
It's a huge factor! Reduce your stress levels and it will help reduce your symptoms for "Dermatographic Urticaria" I.e. dermographic skin.
Can get at CVS or other pharmacy - it cools burning sensations and helps your skin heal, so your symptoms subside faster. Works for me!
I hope this helps! :)