Use the method of initial rates
Compare how the reaction rate changes when reactant concentration changes
If doubling a reactant concentration doubles the rate, the reaction is first order in that reactant
If doubling a reactant concentration quadruples the rate, the reaction is second order in that reactant
If changing a reactant concentration does not change the rate, the reaction is zero order in that reactant
Write the rate law from experimental data
Sum the exponents in the rate law to get the overall reaction order
Use integrated rate laws and concentration-time data
Check which plot is linear
A linear concentration vs time plot indicates zero order
A linear ln concentration vs time plot indicates first order
A linear 1/concentration vs time plot indicates second order
Use units of the rate constant
Zero order: concentration per time
First order: per time
Second order: inverse concentration per time
Use half-life behavior
Constant half-life indicates first order
Half-life changes with concentration for zero and second order reactions
Confirm with multiple experiments for consistency