Soaking fruit, veg and flower seeds for 12 - 24 hours before planting them will help to soften the tough seed casing, meaning you'll see results sooner. Plus doing this means that you don't have to worry about watering too little / too much in the early days (whilst you can't see what is happening below the soil) as you'll know the seed has had a good soak and has absorbed plenty of moisture already.
Use cool water from the tap, enough to cover the seeds by half a centimeter and leave them to soak overnight. Make sure that you label the jars you use - this is a good writing activity for children to assist you with.
If you want REALLY quick germination (if you have a yet-to-be-hooked-on-gardening child helping you for example) then soak pak choi seeds overnight and by the time you come to plant them they will be sprouting already! Once planted they will be showing a proper green shoot after being in the soil for just one day. Wow!
Other quick sprouters are (pre-soaked) mangetout-peas, rocket and sunflowers. They will poke their little green heads up out of the soil within a few days.
We wait until May (up here in the North of England) before sowing any seeds, otherwise the young plants get 'leggy' (straggly and desperate for freedom) whilst we await the end of the overnight frosts.
Happy gardening!