For SW book when you see a price you are comfortable paying and then check back for price drops. At least then you can rebook and have the opportunity to save points or spend those travel funds on another fun trip. (And if you can't use the funds within the year, then at least you were comfortable with the price to begin with)
Popular days, times, routes may only go up as seats sell or they could have price drops as sales come out. It's really hard to predict. Sometimes just being cheap makes a route popular and it doesn't really change as you might expect. If it's a less popular day, time or route I usually see the best pricing about 6 weeks out. But if you're going spring break I would not wait until then to book. Your cheapest options will usually be Tue, Wed, or Thu flights.