The first step in germination is to select the strongest seeds. Traditionally, the seeds are added to salt water and floating seeds are discarded.
The less salt, the less floaters. If you don't have many seeds, use clear water. I did and still had 99% germination.
If your rice has weevils, this is a good opportunity to find out! They don't like being immersed in water (especially salt water) and will come to the surface. If you discover weevils, put your rice seeds in the refrigerator. It won't kill them, but they will become dormant. Refrigerated storage is a good idea, in any case. If you have time, find some weevil free seeds.
You may be able to germinate the rice, even if the seeds contain weevils. But, I feel much better starting with seed that is weevil free.
Once you are satisfied with the quality of your seeds, you can plant them in the flats.
One seed was placed in each cell, then gently pressed in with a blunt dental tool (or a pencil or stick). Then I sprinkled some dry starter over the top. Covering some as deep as 1/16" and others barely at all. I don't think that rice requires light to germinate, but it may. It certainly requires light once it has emerged from the soil. And it will germinate more quickly in warm starter mix.
Rice likes warm weather and sunshine. When I was starting mine, we had some unusually cool, rainy days. On those days, I brought the container indoors (handles!) and heated it with artificial lights. I put a floating thermometer (for tropical aquariums) in the water. I never let the water temperature go below 65 degrees F. Optimally, the water temperature was around 85 degrees F.
To keep the bed warm, you can add warm water to the container. I heated spring water on the stove. On cool or rainy days, artificial lamps provide light and warmth.
8mm Movie camera light fixture on old telescope tripod. Two flood lamps & two plant lights.
Standard heat lamp.
Germination time varies. I kept my plants warm and some were almost 6" tall, twelve days after planting! If you germinate your plants at lower temperatures, they will probably be fine but will take considerably longer. A good rule of thumb is, don't let the nighttime temperature go below 60 degrees F.
Base your germination timing on your location. Rice has a fairly long growing season. The earlier it is transplanted to its final location, the sooner the heads will develop. But, too early is no good either. Plant your seeds two weeks before all danger of frost has passed. In our area (southern Ohio) May 8th is our last frost date.
As the seedlings develop, the roots will grow through the holes in the bottom of the cells and into the water. They will be ready to transplant when they are around 5" or 6" tall.