For a delicious marinade we use - tomato sauce, chutney, mustard, garlic, olive oil, salt+pepper, honey +lemon juice, mix into a nice paste, leave them out of the fridge, they braai better if not too cold
Cook a steak gently at first and finish with a sear. (Not sear first to "keep in the juices" - that's an old wives'' tale!) It will have a darker deeper crust and also be cooked more evenly from center to edge.
Keep it simple. Buy good quality meat. Remove the meat from the coals before you think it is done. let it rest before cutting. And stay away from marinades in a bottle (expensive) - make your own (tastier, healthier)!