Old question, but I have some insight that might be useful.
Not a chemist, but enthusiast, and there seems to be two types of info to know, scientific and practical. For example, knowing that adding sodium hydroxide to water makes it heat up, an exothermic reaction. Meanwhile, practical might be knowing that you have to occasionally vent separatory funnels.
Imo, look at how the chemicals you want to make are produced. So you could look at meth, and see it is made from ephedrine, and p2p. Then you look at how each route works, ephedrine has iodine and red P, as well as lithium and anhydrous ammonia.
P2p has mercury amalgam, the n methyl formamide, borodhydride, and precious metal catalysts.
Now, you look at how chemicals that are similar might be produced. This is where scientific knowledge is needed, to know how things work, but you can often extrapolate and practically try various routes, if you don't mind wasting money and time. You'll still need scientific knowledge, and while I don't know it very well at all, TLC can help determine how a reaction is proceeding.
For example, mdma is produced very similarly to meth, and most routes are similar enough. It gets iffy though, if you don't have enough scientific knowledge (me included) to really know how the mechanics work.