You can
marinate (one suggestion) or season it, your choice.
Tri-tip is a tougher cut that is usually cooked to med-rare/med. Because of this, it benefits from a slow rise in temp* so, imo, is best cooked slowly to a point, say, 7-10? shy of your target temp, then seared directly to finish. It should then be rested, tented, about 10 minutes before slicing very thinly against the grain.
Kevin
* There are a couple key enzymes in beef that do much to make it tender. These are the same enzymes that work during dry- or wet-aging. Their activity increases as temps rise - but stops once temps get too warm (one stops at 105?, the other at 120?). Milking the time before the enzymatic activity stops can offer benefits, especially to cuts cooked to lower internals.
Leave the meat out to warm towards room temp for 90-120 minutes before cooking. Then cook at low/slow temps (on a grill or in a WSM use a mini-Minion start) at 225-250 to an internal of, say, 120-125, depending on desired finish doneness. Then sear the meat both sides over direct heat to develop surface flavor. Rest, as noted, slice and serve.
This same technique is good for other similar cuts cooked to low internals, like the cuts from the round (including 'sirloin tip', which is actually a cut from the round).