The potting soil, in this case, should contain some real soil or compost to supply living organisms to work on the seedcoats. Nicking seeds with a file or carefully nipping at them with a wire cutter also lets water penetrate.
The easiest pretreatment is that needed by many grasses and most annual flowers and vegetables. Seeds of these plants need nothing more than a period of dry storage of from one to six months before they'll germinate. Cold is not needed but does keep them fresh longer, so my vegetable and flower seeds are waiting out winter sitting in airtight plastic boxes in my garage.