Tri tip steak, being lean, can easily dry out and turn into a strip of leather if not grilled carefully. However, marinating the steak before grilling can effectively prevent that.
At least half of your marinade should be made up of oil, be it neutral or flavored. For every two parts of oil, add one part of some acid, like lemon juice, and no more than that.
Add seasonings like herbs, chiles, or garlic and optionally, some sugar to help the meat caramelize on the grill. The salt you add can be in the form of something like soy sauce.
Once you have the perfect mixture, marinate your steak for at least one hour. You can go up to 12 hours or even overnight, but marinating your steak for days can ruin its texture.
The salt in the marinade will help the meat’s proteins retain their moisture, and the seasonings will add more flavor. The fat will also keep the meat moist and help it brown well.
As for the acid, many believe it helps tenderize the steak. Although some say it can make steak mushy, that happens only if you soak the meat in an acidic marinade for too long.