when to start studying for OAT?

Sorry for the second post in a row. Again I am a freshman in a 3/4 program so i am graduating from my undergrad in 3 years, applying to optometry school at the end of my sophomore yr next year. by the end of this year i will have completed bio 1000 & 2000 and gen chem 1 & 2. next year i will be taking orgo 1 & 2 and bio 3000 and Physics 1 & 2 and microbio/biochem.

When should i start preparing for the OAT? Should i start preparing after finishing bio 1000 & 2000 and Gen chem 1 and 2 this year? What do you guys recommend using to study?