Platyceriums grow fairly slowly compared to other ferns, especially during the early stages of their lives, so they will spend a long time in the place where you first sow them. It's important that you start them off with the proper conditions.

Soil: I use a mixture based upon plain peat moss, though I've found that coir (coconut husk fiber) is also an excellent base. Do not start with pre-made soilless mix or potting soil, as these frequently seem to contain composted materials that break down rapidly into a slime that is deadly for epiphytes like staghorns. Three parts peat to one part perlite is fine; if I'm feeling like being fancy I'll add some sphagnum moss and horticultural charcoal (I haven't really noticed any significant benefits from these materials, though).

The soil mixture should be pasteurized, to kill any insect eggs and retard the development of mosses, fungi, and algae as long as is practical. Wet the soil, and microwave it in a plastic bag or covered container until it is good and hot. Let it cool off for a while, then nuke it again for good measure.

Pots: Use whatever size of clay or plastic pot is convenient (4 inch pots have worked well for me). The pots should be sterilized, too. Plastic can be soaked in a 10% bleach solution for half an hour, clay can be boiled or microwaved.

Sowing: After everything is reasonably sterile and cooled off, fill the pots with soil and sow the spores. Since spores are just single cells, it can be difficult to spread them evenly, and not so thickly that the sporlings choke each other out. Gently shaking them out through a fine mesh is a good method to try. I don't attempt to sterilize spores, by the way, as it is a lot of trouble, spores tend to be lost in the process, and it isn't necessary with the methods I use.