[DIYbio] Increasing production of compounds already present in a plant?

How would you get a plant to produce more of a compound? Increasing the amount of caffeine in coffee, antioxidant anthocyanins in berries, or even that cyanide precursor in apple seeds?

I'm assuming that it depends on how the chemicals are produced in the plant of course. When I googled caffeine biosynthesis for instance, I saw that it involves several different steps. I'm guessing if you're using genetic engineering techniques it'll be hard to figure out exactly where your production is bottling up, but still the idea would be to increase the amounts of the enzymes needed in caffeine's sake at least to produce theobromine and turn it into caffeine. And I thought that you could increase the amounts of the enzymes (N-methyltranferases I think is what i read and add theobromine to the plant and let it turn that into theobromine into caffeine, but that's lazy! :D. How do you get an organism to produce more of an enzyme? Or I guess more completely, I don't want to know how to add a new biosynthetic pathway, but to increase the efficiency of one already present. I guess if it's too specific to the pathway in question, then stick with caffeine. Anthocyanins sound too tricky from Wikipedia (several enzymes at once) and I'm not interested in poisoning anyone so apples won't be much use.

Also slightly unrelated question but I don't really want to be making two posts and it's in the same vein, genetic engineering and compounds that plants produce, but if a plant produces a chemical in only its roots, or its leaves or its fruits, how would you get it to produce that compound in other parts of the plant? Is that a function of epigenetics? I'm thinking of things plants produce like insecticides and aromatic compounds.