Plants with heads similar to blackeyed susans and coneflowers should be allowed to dry on the stalk which will allow the head to fully expand, allowing seeds to ripen and making it easier for them drop out. Once you have gathered the seeds you wish to save, the next step is storing them. Proper storage is key to how well they will produce next year. The main thing to remember when storing seeds is to keep them cool and dry. The best place to keep your seeds is in a paper envelope, as they allow air in to keep the seeds dry.
Moisture can cause mold and speed up the seed's biological processes.
Be sure to label your envelope with the seed name and the date. Once you have the seeds in the paper envelopes you can then store them in an airtight container if you wish. Harvesting your own seeds involves trial and error from season to season. The methods of harvesting mentioned above have been around for a long time and prove to work well, and as long as you take care to store them properly the results are very rewarding. When you harvest your produce from your garden you can harvest next year's seeds right along with it using these methods.