Research the laws in your city, because laws governing solicitors can vary from place to place. In some cities, it is against the law for solicitors to come to your door without having a permit. If credentials are required in your area and a solicitor comes to your house without them, report him or her to the local police immediately.
Post a sign that clearly states you don't want to be contacted by solicitors. Some solicitors feel that it's still worth a shot and will knock on your door anyway. But in some areas, solicitors can be charged with trespassing if they fail to take heed to one of these signs.
Write a letter or call organizations that are soliciting you by mail. Often a person donates to a charity out of the goodness of their heart only to be bombarded with letters requesting more money. By contacting the charity directly you can let them know you'd like to be taken off of their mailing list. You can also ask them if your information was provided to them by another source. If you find that to be the case, get that organization's contact information so you can call or write to them and repeat the process.
Refrain from giving personal details to companies or businesses that ask for it unless you are fully aware of how the information will be used. Internet surveys or questionnaires that you fill out when participating in drawings are two ways in which information can be extracted from you willingly. The bad news is that many times this information is then sold to solicitors that try to sell you products based off the answers you provided. You can prevent solicitors simply by keeping your personal information out of the wrong hands.