light and warmth.
using a carton - cut one side of the container so that it can be turned up. write the name of the seeds that you planted on the flap. see the image above.
drainage is another feature to provide in your make-shift planter. store bought seed starter trays come with drainage and, many times, a tray, so do what you can to mimic this feature and provide drainage for your seedlings. if too much water is added to the soil and there's no way for the excess to drain, then your plants could die.
provide light to the seedlings. if you cannot provide sunlight, then do the best you can 