I find this method works well for brassica seeds:
Take some multi-purpose compost, add about a fifth by volume of perlite or vermiculite and a light dusting (like icing sugar on a cake) of lime. Mix well.
Fill a half seed tray or a small pot and firm it slightly
Water well and then drain (I float the half seed tray in a full tray of water)
Thinly scatter the seeds on the surface and then lightly pat them with a finger so the seed is in good contact with the compost - not pressing it too hard though.
Thinly cover with vermiculite - just enough that the surface of the compost is hardly visible.
Place in a propagator at 20ºC - optimum germination rate is achieved between 10º and 25º
Once the seedlings are about 3cm high, prick out into 3" pots. I like a mix of 50/50 by volume of multi-purpose and John Innes No2 with a little lime added. I plant deeper than they were in the seed tray, about half way up the seedlings stem.
Harden off gradually and plant out when a reasonable size. If club-root is a problem, it can pay to move into a larger pot to allow better root development .
There's information that will help here:
Optimum Germination TemperaturesGrowing Brassicas