If they are planted too deeply, they may not germinate. A spray bottle is handy for wetting the surface without washing away tiny seeds. Waiting even a couple of days can cause the seedlings to stretch so much that they will never be as sturdy as they should be. Fluorescent lighting is ideal because you can control it. Keep the lights on about 14 hours every day.
Warmer temperatures can cause rapid, weak growth.
Excess nitrogen fertilizer can cause weak growth. Seedlings generally do not need fertilizer until they are transplanted from the seed tray or when they have 2 sets of true leaves. Damping off disease is a common cause of seedlings keeling over and dying. This fungus thrives in wet soils that are high in nitrogen, so avoid overwatering and don't fertilize until seedlings are transplanted. Always use sterile, soilless propagation mix, and sterilize seed-starting equipment before planting by washing pots, trays, etc.