Swiss chard is an interesting micro! They are actually compound seed pods and can be sensitive to over watering during the germination process. A short soak is ideal, 4-6 hours, nothing grand, and they will perform the best in soil with a light soil cover. This is where it gets a little tricky - the medium should be just barely moistened. If too damp it will over soak the seeds during the germination process resulting in a thinner crop. You will want to lightly mist and only water unless absolutely necessary. You will find that as the root structures grow, you will need to increase the amount of water provided. But they should be borderline dry during the first 3-4 days. Humidity dome is also fine to use to help regulate moisture. They will germinate rather unevenly, especially the rainbow mixes - be prepared to give them a few extra days to even out and try to grow them longer for a more uniform looking crop (usually somewhere around the 21 day mark.)