Dealey Plaza and the Sixth Floor Museum cover JFK's assassination—heavy but worth it. Then get out of downtown and hit the neighborhoods.
Deep Ellum is where the music and weird art are. Dive bars, tacos, murals on every wall, crowds that show up after 10 PM. Bishop Arts Village in Oak Cliff has the coffee shops, vintage stores, and restaurants people actually drive across town for.
The Dallas Museum of Art is free and bigger than you'd think. Perot Museum of Nature and Science works if you've got kids or just like that stuff. Klyde Warren Park sits on top of a highway and connects downtown to Uptown—food trucks, events, people-watching.
Spring (March to May) and fall (October to November) have tolerable weather and stuff happening everywhere. Summer is brutal—100+ degrees from June through September, and you'll melt walking between your car and the door. Winter's mild, and you'll score the best flight deals December through February. Just pack a jacket for the random cold snaps.
DFW Airport is massive and sits between Dallas and Fort Worth, about 30 minutes from downtown Dallas, depending on traffic. For cheap flights to Dallas, stay flexible with dates and compare everyone. Budget airlines hammer this route, and even the big carriers discount it because getting seats matters more than fare class here.
Dallas is big, loud, and moves fast. Show up ready for that, or you will feel left out.