12th grade - There will still be some opportunities available for seniors at the D-III level all the way up to the time college applications are due at the end of December. If you are still seeking to play at a D-III school, you will want to attend the December D-III camp, so you can be seen by as many coaches as possible. Reach out to D-III coaches and send a video during the fall months to determine possible interest.
If you are a young senior or a fairly late bloomer, continue to work hard on development. If you think you would like to play D-I or D-II, reach out to coaches with a video of your play to see if you would be good fit for a D-I or D-II program. If so, you may still be able to find an opportunity by considering doing a Post Graduate year at a private high school (prep school). This would essentially push your recruiting class back one year, and you would follow the recruiting advice which is recommended for 11th graders.
If you know before your senior year that you would like to do a post graduate year, then attend the July Super Sixty Camp as a Rising Junior. You will also want to attend the December Junior Camp.