I keep learning about this germination thing. My success rate is good, but not 100%. This is where my head is at at this point - just my 2 cents after studying this thing for a couple years:
1. Temperature is important no matter how you germinate. Success is highest above, ~24C. Cocoforcannabis recommends 30C, which I shoot for. This means that if you plant direct to final pot, you need to bring the pot up to temp for a day or two before planting. Seeds seem to vary in their temperature needs, but it seems none of them mind a warm start. I now use a seedling heat mat controlled by an Inkbird to deal with temperature.
2. I use the sandpaper tube to scratch up the seeds before wetting them. I have used everything from a couple quick shakes to a minute of vigorous shaking, and don't know if that makes much difference. The aim here is to assist in the seed coat softening up by improving water penetration. It is also possible that this may abrade the seam that splits, making it easier for the plant to open it. Cocoforcannabis recommends a very brief shake to avoid "damage to the seed" although for the life of me I can't see what that damage would be. I have shaken seeds until much of the pigmented coating of the shell has been abraded off with no sign of damage to germination. Also, I have heard of some growers actually using a nail file on seeds that they find particularly difficult to persuade to open. At this point, I doubt that anything short of actually damaging the embryonic plant inside the coat is likely to hurt. But hey, I am still learning.
3. After abrading, I start with a soak in ~1/3 peroxide (the stuff from the pharmacy used for first aid, it is 3%) and distilled or RO water. I have varied the length of time from a couple hours to 6 hours or so, and do not know whether either end has a big advantage. the Cocoforcannabis crew recommend keeping the soak short because once the seed activates, it needs oxygen, and may run short if it is submerged. The peroxide may accomplish a couple things, one being presence of oxygen in the water, the other being killing off or discouraging any pathogens in the water. It might also help with getting the seed coat to soften up, I dunno. This soak is done in about 2 ml or so of liquid in a plastic egg carton heated on the heat pad in the germination tray. Less water means better oxygen.
4. After soaking, the seed goes into a wet paper towel or cotton cloth holder that holds the seed vertically so the root has less tendency to burrow into the paper towel. I have tried the cotton option to avoid the possibility of bleach or other contaminants in paper towel, but do not know if this is an issue or not. Again, this is done in the heated germination tray. Once the tap emerges, the seed goes into a peat plug already soaked and warm in the tray. Once the tap root shows out the bottom of the plug, it goes into its final pot, which is already up to temp.
Lots of peeps just plant direct and it works most of the time with most strains. The advantage is simplicity, the downsides are that the larger initial pot can cause difficulty controlling moisture, may result in poorer root colonization of the pot, and makes initial temperature more of a chore. Before you decide on any of this, a serious look at the germination information on Cocoforcannabis.com would be a good idea, that crew knows their stuff.
Happy growing all.