...
Maximize the input amounts of RNA where possible.
Use 1 hour incubation time for reverse transcription (step 4).
Use 48 µl of Purification Solution (PS) at step 16.
...
Perform a qPCR assay to determine the optimal cycle number for library amplification.
...
See these FAQs for further details:
What do I need for the qPCR Assay?
How do I calculate the Endpoint PCR cycle number from the qPCR assay?