A Perfectly Leisurely Timeline
The best plan begins at least 18 months before you plan to start law school. This gives you time to study for the LSAT given in June before the year in which you want to start school. You'll know your score well in advance, and can plan to take the test again if necessary. You'll have time to research schools thoroughly, meet with admissions officers at planned events, write, rewrite, and polish your essays, choose your recommenders or evaluators, and learn the ever-changing Law Services application software. Here's what such a plan would look like:
The Perfect Plan for Applying to Law School
Of course, your time won't be spent quite so rigidly. You can prepare essays when you're tired of studying for the LSAT, and you'll almost certainly take some time off from studying to explore law schools when the U.S. News rankings are released in March or April. Reading law school books and otherwise preparing to begin law school will stretch from March to July, but you'll have the time; after all, paying seat deposits will only take a day out of April.
The plan above is ideal, and like most dreams, matches the reality about 10% of the time. Many people will have problems to address, complicating the timeline just a bit. A more pragmatic plan for the early applicant looks like this:
A Reasonable Plan for Applying to Law School
This plan is entirely reasonable, assuming that your first LSAT score is only a few points lower than your target score. Most people dislike retaking the LSAT, but at least you have plenty of time to apply to schools with February deadlines once your second score comes in.
If you're starting too late to take the June LSAT, you'll need a different plan, of course. Here's what to do if you're planning to take the September or October LSAT.