Dampen the mix to the consistency of a rung-out sponge. It should be wet, but not dripping, with no dry lumps.
There are many good potting mixes available. Using a soilless potting mix rather than outdoor soil is preferable because potting mixes don't readily compact, don't contain weed seeds and don't have disease spores and other possible problems.
Also, since new seedlings don't require fertilizer until they sprout their first true leaves, you don't really need a mix with fertilizer already in it.
