For the past year or so, the fares on "opening day" have been terrible. Usually they come down within a week or so. I typically have "ticketless travel funds" floating around. These are credits that I receive from SW when there is a fare decrease. I don't have to pay a fee to make the changes, so I check my SW fares daily (sometimes more than once). If the fare goes down, I change my flight to the new lower fare and have a credit for future use. I only book the "web only" or "wanna get away" fares. The higher fare classes are way more $$ than I want to spend, but they are fully refundable.
I always, always, always, book two oneway fares. This was if only one portion of my flight fare decreases, I can change it without risking the other portion.
I always check kayak.com to see what the other airlines are charging for the same ticket. If I can get SW a little higher than the others, I will book it. If not, I will wait. Remember to factor in baggage charges and the other Hidden fees with the other airlines. Southwest doesn't charge for checking 2 bags, so the savings of that fee alone can be worth it.