placing your art work with another person to hold the work on the wall. it's easier to judge the correct height from a few meters back
brick walls drill into wall using a masonry drill bit, then hammer in a wall plug, then screw in a screw.
plaster walls drill a small hole into the wall. if there wall is hollow drill in a wall plug and then a screw. if you find the stud drill a screw into the stud
clean up impress your other half by holding a dust pan against the wall under the drill while your drilling.