In a lot of cases there are rules of thumb that will give you a degree of success providing you provide the basics.
- Seed (must be viable) and prepared correctly
- Pre-treatment (where needed)
- Soil
- Light
- Warmth
- Water
- Time of year (Season)
- Germination Time
One of the most neglected basics is time of year. Unless you can provide year round light, warmth and care, do not sow seeds out of season. Another one is patience. Seeds do work to a clock, just not yours. If you dont allow sufficient time or you are impatient to get going, then you will not have a lot of luck with seed growing.
Season
Season, or more properly growing season, is taken to mean when the soil is warming and the days are lengthening towards the summer highs. Indoors this means anytime after the winter solstice, as the days are lengthening nicely for the seedlings to subsequently grow away. Outdoors it is when the soil is sufficiently warm for seeds to come up (rule of thumb, if you see weed seedlings coming up, its time to plant your seeds). Yes some seeds can be 'tricked' by artificial heat or artificial light, but not all can often appearing to have inbuilt calenders and will only germinate at a certain time of year.
Timing
The time it takes seeds to germinate varies wildly. In some Cactus this can be a little as 18 hours, in some plants such as palms and hardwood shrubs in can be up to 18 months. There are things you can do to speed things up, but where a minimum time is quoted, this is the minimum for treated seeds. There is no point expecting anything before that point, or being disapointed if you have to wait till the maximum time. Thats just nature, so work with it, not against it. Rule of thumb - never give up unless you can see that the seeds have clearly failed - ie they have rotted.
