Maryto, the number of strands to use depends on the project and the stitches. Is it counted cross stitch? You use more strands for lower thread count. The patterns should tell you how many to use, but if not, you could stitch a small part of the design with 2 or 3 strands and see if it looks nice to you - good coverage without looking bulky.

Hope this helps! Donna

I've always used two threads for regular embroidery unless it's outline stitch or back stitch and use one thread and small stitches, especially around corners...more effort, better results.

I usually only use 2 threads too, unless you are filling in a large space like a flower petal then I use 3.