I sign up for a lot of
newsletters, because most companies will notify you of sales/events/coupons/GWPs--I just thought of brands/products I bought (or am thinking of buying) and sign up on their website.
I also visit magazine websites (insidevogue.com, AllureAccess.com, shopetc.com) and many of them list deals. There's usually a page in all fashion magazines that lists sales/events and I check those too.
I'm also signed up for
newsletters from: dailycandy.com, sheckys.com, topbutton.com, clothingline.com, newyorkmetro.com, and eversave.com which list sample sales.
Wow-coupons.com always has a good list of retail store coupons, as does citylaunch.com.
Plus, I hear about some things through friends.