1A) Make sure your current equipment is up to snuff: Essentially, inflate your tires to the correct pressure for your vehicles. For towing, that isn't the value listed in the door jam either. If you don't know that information, you can simply inflate your OEM (or equivalent) tires to the max pressure listed on the side of the tire (on both the trailer and the tow vehicle). Other safety equipment like a trailer brake controller should be installed.
1B) Make sure your tongue weight is at least 10% of total trailer weight. Even more would be preferable.
2) After those first two steps, you can then consider adding anti-sway and weight distributing hitches. There are a wide variety. Your vehicle should tow fairly stable before even adding one.
3) One you've performed those other steps, you can fine tune to your hearts content. Many people upgrade their tires on their trailers right away. Many people driving half ton tow vehicles upgrade their P metric tires to LT rated tires too. People also often add air bags to enhance the rear springs of their tow vehicle. Lots of fun ways to spend your hard earned dollar.