I usually try to call the slope interchangeably delta y / delta x OR change in y over change in x. The it doesn't matter which they do first: -2/3 is change y by -2 and change x by 3. So long as they know which is which they can still choose to change x first and read that change as 3 with an associated change in y of -2. Finally re-express -2/3 as an equivalent ratio such as 4/(-6) and you can still correctly locate another point by "simultaneously" changing y by 4 and x by -6.
Moreover I emphasize that the slope is a rate (ratio) as usually indicated by the key word "per" which indicates a quotient (cf. miles per hour, price per pound, per cent, etc.) From these I indicate the "clues/check" that positive rates indicate increasing and negative rates indicate decreasing.