I start a bout 3-4 months before my local comp and write out a "brewgenda" with the beers I plan to enter, the tentative schedule for when those beers will be brewed, then I acquire the ingredients I'll need and start brewing.
I admittedly game the entry process. I have taken first in the English Bitter category 6 out of the last 7 years. I brew an ESB (strong bitter) all the time just to drink, but for the competition I also brew a Best Bitter and Ordinary Bitter. They have also combined the bitter category with English Commonwealth beers since the 2015 guidelines came out, so to encourage them to split those categories I also enter an English Golden Ale and English IPA, this year I'm also entering an Australian Sparkling ale. If they don't split it gives me a few more shots at hitting my goal of taking 1st, 2nd and 3rd in the bitter category, although I really want to do that with bitter, not the commonwealth beers.
Right now I have two more batches to make before the Aug 19th entry deadline. I'll have 10 entries.