Offer extra value rather than a discount... e.g. Book a standard mani and get a free upgrade to luxury Manicure, free express facial with every massage, free gel upgrade with any mani/Pedi, free Brow Shape and Tint with lashes (remember to take photos of brows Lashes and nails to pop on Facebook Instagram and twitter, this generates a lot of custom)
If you have any prebuilt packages (brows and lashes etc) make a point of promoting then rather than offering further discounts
Bring a friend for free (friend must be a new client and enjoy services of the same value) this way yes your literally doing it half price, but you're doubling your chances of long term clients