The most important thing about alchemy is doing your research. Few of Gaia's features will punish you for ignorance quite like Alchemy.
If you haven't read it yet,
An Introduction to Alchemy is a great place to start so you can understand the basic nuts'n'bolts of the feature. From there, check out the
Ultimate Alchemy Formula Guide; each page is dedicated to a different level of Alchemy, and includes a post listing the easiest/cheapest formulas to make on each level.
If you ever find yourself confused about some aspect of Alchemy, there's probably a link to a guide that explains it in
The Alchemy Guide and Information Database.
Good luck, and remember patience is key!