I would start with your current clients. Let them know that you are currently in a position to take on more clients and you were wondering if they had any colleagues that may be interested. Referrals and word of mouth are the best advertising you can have. If they don't, ask if it's ok to use them as a reference. That way you know ahead of time. There are a lot of marketing tips on the forum here as well. If you go back and search you will find a ton of suggestions.