Take Stinky's advice to heart, anytime you hear it. She isn't going to steer you wrong.

Only ONE seed per pot.

Cannabis grows extensive root systems, and in fairly short periods of time. Letting them get past the seedling stage without transplanting into individual pots is almost certainly going to force you to separate the roots. Most likely damaging them, and stunting the growth of the plant.

Smaller pots.

Smaller pots need to be tended to more frequently (watered more often), but you're not as likely to overwater, which can drown young seedlings.

Finer soil.

Lots of compost, while certainly good at allowing air-pockets to form, aren't suitable for growth by itself because it's not really soil that you're using...it's composted materials, sticks and bark.

Water gently, don't spray.

Spraying the topsoil is good for temporarily moistening the topsoil, but it will dry in no time at all. Small seedlings shouldn't dry out, because it's far more difficult for them to survive than an established plant that's already retaining lots of moisture.

Seeds must be planted at a depth of 4x their diameter (in this case, no deeper than 1cm) and kept moist , not soggy, until they sprout.

Taproots, while predisposed to growing downwards due to gravity, can also have a hard time penetrating the topsoil without any weight placed over them. When sowed into the soil, the taproot reaches deeper down into the pot, and enough pressure will form to push the seedling out of the soil.

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Read Stinky's signature, and spend lots of time reading through the extensive FAQ's, as well as previous posts archived in the forums. There's such a wealth of information here that it would take several lifetimes to be able to digest it all!