Even after you book keep checking rates as they do fluctuate. Of the numerous times I have rented I have almost always gotten a better rate then what I started with.
This past Aug at LAX I originally booked 9 days and the rates were over $400 for a Rav 4 sized at all agencies. I then got it down to $370 at Avis and eventually $340 at Dollar. I used discount coupon codes that I talk about below.
Sign up for each car rental agencies special club, which are almost always free. They sometimes have special rates/discounts, but more importantly depending on the airport may have a special desk/are where you can go to get the car and not have to wait in a long line.
Do a web search for "Alamo car discounts", "Avis car discounts", etc. Sites like Retail Me Not will pop up with discount codes that you enter in. If you have AAA check that too.
At LAX I believe all car rental agencies are located off site so you will need to take a shuttle.