as you should already know, istarian resources and level advancements are based on tiers. for instance, taking blacksmith from level 1 to level 100 would take you from crafting in tier I resources (tin and copper to make bronze, for metal) up to working in tier VI materials (adamantium, very rare and difficult to find).
trainers sell - depending on the particular trainer - beginner (usually covering tiers 1 and 2), journeyman (tiers 3 and 4), and expert (tiers 5 and 6) formulas. you need to have the minimum required skill level for the form you are scribing in order to use it. for instance, you would need to have at least a 400 in skill level to scribe (and make items) that use the metalworking skill in the journeyman blacksmith advancement - in order to scribe and use a journeyman metal bar form, for example. the forms for each advancement covers the levels below it - so, the expert metal bar form covers the making of all tiers of metal, while the beginner form only covers the first two tiers.
trainers also give quests, as we already know. these quests will get you a good distance along, but you will still need to do a lot of grinding to get to each tier. for my money, making and deconning tools at the max skill level you can do is the best way. if you have access to player workstations - in game workstations do not give a bonus to your skill - you can use the bonus from them (as you might imagine, player made workstations can be beginner, journeyman, or expert, and give an according bonus to use them. therefore, it is possible for a beginner blacksmith to scribe a journeyman form, if done while inside an expert workstation.).
of course, this process works the same for all schools, both adventure and crafting. and for dragons, as well - they can use lair workstations to the same effect.
and that takes care of this bit of bizniz i forgot to do first, before starting the trainers. so, that means that i will be returning to our regularly scheduled madness next time. see you soon!!