Fertilzer for my lawn

What is the best fertilzer to green up my lawn and make it thick grass? I have St. Augustine grass and it is thin. When it rains my grass turns thick and lucious. How do i get this effect on my grass?

a good natural fertilizer that will also prevent weeds is corn gluten meal...also helps to kill grubs in the soil and therfore moles and gophers.... you can usually find it at a farm or feed store.........there is another excellent natural product that has a wonderful smell when you first put it out it is dried molasses..... the brand I find in my area is call Mor Lasses.....it doesnt do anything that I know of for weeds but is a great feeder for the plants andgrasses