For me by far the best advert has been word of mouth, but I appreciate you need to get going in the first place.
A lot of my initial clientele came from having cards in the local hairdressers....she has cards in my studio, but if mobile you could offer a free set of nails.
Yellow pages has been OK....but a lot better since I upgraded my advert to more than just one line. the money I've had back from it paid for itself in a month or two.
I also put up a couple of treatments as raffle prizes in local charity fund-raising events, on the basis of being able to put my cards out at them.....one person never even claimed their prize, yet in the last 2 weeks I've had 6 new customers from that alone.
And rather sadly, I'm just a card tart....I give my business card out to anyone and everyone. if I go for lunch somehwere I pay and give them a few cards...ask if they can pass them around. Invariably these places, as you are a customer of theirs, will put your cards out. I paid about £50 to get 5000 cards printed from Vistaprint, and that seems like a lot of cards, but think about it this way....it only takes 2 or 3 customers to pay for it, and if you are scrimping and saving where you give your cards too (I know quite a lot of peopole go for the 200 free ones) you''ll not get much back then.
I even give cards to the (female!) assistants on the checkouts at the supermarkets.....they usually keep their nails short for work but love a nice set if they have a function coming up!