What should I take into consideration when designing my custom primers for reverse transcription or 2nd strand synthesis?

First Strand Synthesis
Any primer used for First Strand cDNA Synthesis has to be designed with a partial Illumina P7 adapter extension. Adapter sequences are kept short pre-PCR to allow for efficient removal of short fragments during the purification step (steps 12 and 16). The full Illumina P7 (Read 2) adapter sequence will only be introduced during PCR (step 28).
Partial Illumina P7 Adapter Sequence (Read 2) for First Strand Synthesis Primer:
5' GTTCAGACGTGTGCTCTTCCGATCT – Target sequence 3'
Here the target sequence has to be the reverse complement to the mRNA sequence in question (=cDNA). The chosen target sequence should be as specific as possible with a melting temperature (Tm) that is as close as possible to the intended reaction temperature (50 °C). In most cases, 20 nucleotides (nts) are enough. Target-specific primer sequences should not exceed 50 nts. The entire primer including the Illumina Adapter sequence should not exceed 75 nts. The optimal primer length is 45 – 50 nts (25 nt Illumina Sequence + 20 – 25 nt targeted sequence).
We highly recommend checking your targeted primers using the NCBI Primer Blast tool available at https://www.ncbi.nlm.nih.gov/tools/primer-blast/index.cgi?LINK_LOC=BlastHome. Use the Primer Pair Specificity Check and run your primers against the RefSeq database (not just RefSeq mRNA). Primer specificity stringency settings can be adjusted regarding the allowed mis¬matches and positions of the mismatch within the primer.
Second Strand Synthesis
Any primer used for Second Strand cDNA Synthesis has to be designed with a partial Illumina P5 adapter extension. Adapter sequences are kept short pre-PCR in order to allow for efficient removal of short fragments during the purification step (steps 12 and 16).The full Illumina P5 (Read 1) adapter sequence will only be introduced during PCR (step 28).
Partial Illumina P5 Adapter Sequence (Read 1) for Second Strand Synthesis Primer:
5' CACGACGCTCTTCCGATCT – Target sequence (mRNA-sequence) 3'
Here the target sequence has to be the mRNA-sequence in question. The chosen target sequence should be as specific as possible with a Tm that is as close as possible to the intended reaction temperature. In most cases, 20 nts are enough. Target-specific primer sequences should not exceed 50 nts. The entire primer including the Illumina Adapter sequence should not exceed 75 nt. The optimal primer length is 39 – 50 nt (19 nt Illumina Sequence + 20 – 31 nt targeted sequence). The Tm of the targeted primers should be within the range of the potential annealing temperature i.e., between 45 °C and 72 °C. Please note that temperatures below 45 °C should not be used. Introduction of 1 – 3 phosphorothioate linkages (PTOs) at the 3' end of the target-specific Second Strand Synthesis Primer may increase specificity.