Sign up to receive newsletters from embroidery sites, such as emblibrary.com - they frequently have fantastic sales and there are also a lot of free designs. Another site with good freebies is pamelasembroidery.com
My Janome 350e loves Madeira polyneon thread, which I buy from sewphisticatedstitcher.com - their prices are good and service is fantastic.
No matter where you get your designs, there are so many different brands of thread that it can be hard to find the right color. That's where a conversion chart is worth its weight in gold--and here's the best conversion chart I've found:
http://threadchart.info/threadchart.php?f=MADPOLY7.
One major suggestion: Keep your designs organized! Here's an excellent article on how to organize designs on your computer:
http://www.emblibrary.com/EL/ELProje...oductid=pr1735
A word of caution: Embroidery, like quilting, is highly addictive!!! Have fun!