By default, the order of execution is the same as specified in the prerequisites list, unless there are any dependencies defined between these prerequisites.
abc: x y z
The order is x y z.
abc: x y z
y : z
The order would be x z y.
But ideally, you should design your Makefiles so that it wouldn’t rely on the order in which prerequisites are specified. That is, if y should be executed after z, there must be a y : z dependence.
And keep in mind that GNU Make can execute some recipes in parallel, see Mat’s answer.