If you edit this question to give it a budget, I can give a better answer.
Web advertising is the best. Google Ads and Adsense are the best. Google Ads and Adsense are paid services, which suport adverts on 70% of the internet, including mobiles. Social media is suprisingly effective too. Create facebook and twitter pages for your service, and label it as a business. Spread the pages as much as you can so people can see them. This action is free, and not too difictult, and has a high sucsess rate.