I used to use starch before changing to wax.
To prepare the starch, I will mix tapioca flour with cold water
until the mixture become neither too watery nor too sticky. After
that, I would then add in hot water that was just boiled to get the
translucent colour instead of white. If the starch remains white,
it means that it had not been made properly and I remembered
applying them before on my no.4 and causing white spots (actually
is the tapioca flour and water which did not mixed well) to appear
on my uniform.
If LL the training notice came late and there is no hot water, I
will put the mixture into the microwave together with the hot water
that was previously boiled a few hours before.
I don't like spray starch, hear from my friends they have to use a
lot to get the collar of the no.3 to become hard. Wax is not
recommended because it can cause the uniform to have a hole easily
which I have 2 now on the collar of my no.4 (one is burnt by the
candle, the other is after some time of ironing and washing). I
guess something must be wrong with my ironing, I get holes
regardless whether I used starch or wax. 
