If you compound high rank things, it gives no more profiency than compounding 2 low rank things together, it is the number of times of successful compound that counts. So just train as normal, and you will get lots of items from enemies. Just compound them together 1 by 1, randomly. Sometimes you get good things, sometimes you dont, but as long as they are successful, your alchemy lvl will slowly goes up.

If you train at cirrus, you can recycle the vine grass and get some straw mushrooms. Compound 1 straw mushroom with 1 turpentine, this would give you tomato juice in most cases, tomato juice Sp +150!!!