If you've bought stuff from them in the past, they will send you account specific discount codes for their pre-sale. Other people's codes will not work on your account, as far as I know, so you have to have bought stuff. One in November, another in the summer. 20% pre-sale for about 3 weeks, then 30% pre-sale for a week or longer. Most of stuff eligible in pre-sale will not be discounted in their actual sales, which are generally pretty limited imo.