Rule number one is "Trust your gut reaction"; if you feel an instant emotional connection with a painting, that 'wow' factor will last and the painting will bring you years of pleasure.
Consider size, colour, tone and mood; it needs to work within the space. If you love it, can you re-arrange the existing paintings or furnishings to better position the painting? Walk into the room and consider where your eye travels. The wall opposite the door might welcome a large feature painting to give that 'wow' factor; a hallway or kitchen might prefer a group of smaller paintings in a 'gallery hang' to act as a conversation piece and encourage people to linger; a main bedroom might need soft gentle colours or is a great spot for a figurative drawing.
Don't forget the bathroom - looking out on a distant seascape might be just what you need to relax when soaking in the bath. (Check before buying as not all paintings will be suitable in a damp environment) Does your home office need something colourful as a stylish background for all those Zoom meetings? Art for a conservatory needs to have UV resistant paints or varnish and work on paper would benefit from being framed with specialist UV resistant glass.