Booking right away is typically the best policy for any low-cost carrier (e.g., Southwest, JetBlue)-- they tend to release lower fares first and the prices just go up as your travel dates get closer.
Keep checking back, and sign up for fare alerts on Kayak (although you'll still have to check SW directly, as it doesn't appear on Kayak). In the meantime, take a frank look at your options from local airports (consider driving to another, more distant airport if you can find a better rate there.) As soon as you find a number you can live with, book it, and familiarize yourself with the airline's policies concerning what happens if the rate goes down later (e.g., give greater consideration to airlines that will give you a credit or refund if the fare goes down).
*Another tip: If you're flying with an airline that has baggage fees, consider traveling "carryon only." I know it sounds a little crazy -- I used to travel with the world's largest luggage myself -- but I've come around. With a good packing list and the use of some good space-saving tips, my family of four can fit clothes, swimwear and accessories for a week, including cosmetics, toiletries, an extra pair of shoes per person, our breakfast foods and snacks, electronics, toys and books, etc. in four 21" carryon bags and four personal items. We save time waiting for baggage and the stress of worrying about our baggage going missing (or having things stolen from it), and never incur any fees.
