Model is "good" = no pattern in the Residual vs. Fits plot
Step 1: If a linear model is good, use it, you are done.
If the linear model is not good, proceed as follows:
Step 2: check the square root model, the exponential model and the power model and see which of these (if any) are good.
Step 3: find the polynomial model with the lowest degree that is good.
Step 4: c) Choose as the best of the good models in a) and b) the one which has the highest R2
Example Elusage.