20 years ago, when I first retired from my professional career in the "corporate world", and opened my own business, Yellow Pages advertising was the way to go. All of the similar business professionals were competing with bigger and bigger ads. The biggest players sometimes had a half or full page ad. They were expensive, but I do believe they helped because that was virtually the only way that someone could find you if they had the need.
Today, I can't remember the last time I went to the yellow pages to look for a company...I just do a search online. If you haven't already done so, my suggestion is to design yourself (or have it designed for you) a website that covers everything about whatever it is that you do. Design a catchy home page with logos and other relevant information, include description of your services, photos (if appropriate), and contact info, including phone numbers, hours, etc. It wouldn't hurt to have testimonials by your customers of your work. If you are mobile, make sure that's clear, if you have a permanent location, consider a map or directions from strategic points in the surrounding area.
If it seems to still be the trend in your area, you can always go with some reasonable yellow pages ad. Make sure to include some of what I mentioned above. You could also look into radio ads. There's quite a lot of flexibility here.
In the end, word of mouth is your best advertising. If you have a customer who leaves pleased with the service, he may tell a few of his friends and relatives. If you have a customer who leaves and he's unhappy, no matter what the reason or who's fault it was, he'll tell everyone he knows!!!