Look for web sites about homeschooling or sites where teachers and homeschoolers might frequent, such as forums or social networking groups. Often people will tell about free worksheets or materials they have found.
Search online using search terms such as "free homeschool lesson plans", "free homeschool worksheets", free educational material" etc. The results should bring up several web sites.
A few examples of web sites that offer free homeschool worksheets and lesson plans can be found below in the resources section.
If you are looking for worksheets and lessons for a specific age group or grade level, you might want to consider adding that to your search terms. For example, you could search "free homeschool worksheets 4th grade level".
To find specific subjects you can use that in your search as well, such as "free homeschool worksheets 4th grade level math" or whatever other specifics you want to find.
Consider using online sources that provide educational material such as the Library of Congress web site. You can find many useful items that you can print out and use as free homeshool worksheets. These include lesson plans, webcasts, educational activities and more.