Darts has the smallest footprint of any game on this site and the most precise setup. The numbers are fixed by the World Darts Federation and they are not approximate: the center of the bullseye sits 5 feet 8 inches above the floor, and the throw line - the oche - is 7 feet 9 and a quarter inches from the face of the board, measured horizontally. The diagonal from the bull to the back of the oche is 9 feet 7 and three-eighths inches, which is the measurement you use to check the other two.
That means a usable darts setup needs about 8 feet of straight floor, 5 feet 8 inches of unobstructed wall, and roughly 2 to 3 feet of standing room behind the line. Call it 11 feet of run. A hallway does it. A garage wall does it. The corner of a basement that is useless for everything else does it.
Measure the height from the finished floor, not the subfloor, and measure to the center of the bull, not the top of the board. Both mistakes are extremely common and both are permanent once the bracket is screwed in.
Sisal or electronic: the fork in the road
A bristle board is compressed sisal fiber. Steel-tip darts push the fibers apart and they close again, which is why a good board self-heals and lasts years. It scores nothing for you, it makes a satisfying noise, and it is what every professional plays on. It also means steel points and real holes in whatever is behind the board.
An electronic board is plastic with thousands of small holes and a sensor behind each segment, played with soft-tip darts. It scores automatically, which matters more than people expect - most casual players give up on cricket because keeping score is tedious. It is quieter, it is safer around children, and soft tips do not punch holes in drywall. It also registers the odd bounce-out as a miss, and the segment feel is nothing like sisal.
There is no overlap between them. Steel-tip darts destroy an electronic board; soft tips will not stick in sisal. Choose the board and the darts follow.
Protect the wall before you need to
Everyone misses. With a bristle board the question is only whether the misses land in a foam surround, a backboard, a cabinet door, or the drywall. A surround is a foam ring that fits around the board and catches near misses. A backboard is a larger panel that catches wide ones. A cabinet does both and closes over the board when you are done, which is the usual choice for a room that is not solely a games room.
Lighting matters more than it sounds. A single ceiling light behind the thrower puts your own shadow directly on the board. Either light the board from the front and above, or buy a cabinet with integrated lighting, which solves it in one purchase.