My experience - just sold my Montgomery 15. Deliver tomorrow.
Clean up the boat, looking like you would want to buy it. Prepare an inventory of the boat and all that you plan to sell with it. Look at a few ads to get an idea of typical specifications, language used, prices for boats in similar condition as yours. Decide on a price. To high and you may get a few lookers, to low and you'll not want to sell it. Pick a price and then decide what is the bottom number you will accept.
Next take some pictures, and try it out on a few free sights. I tried a typical ad language and got a few looks but no serious takers. Did get 3 obvious scam calls/emails. Be prepared and brush them off - no response.
I got several hundred views and several calls when I changed my script to ..."I want a divorce" and told the story how the boat had been abandoned by the owner for a bigger boat. That it was not any fun sitting in the driveway. How the boat wanted a sailor to take her away. Not sure if it worked. Did get more calls interested. And got the call from the sailor who will be the new owner tomorrow. Took about 6 months from when I decided to get serious about the sale. Can tell you it is a bitter sweet feeling.