Use actual DNA sequences for comparison with your cDNA, which is most easily accomplished using a computer. You need to locate the intron positions.
Design your primers from the cDNA from exon sequences that would be located on either side of an intron in your DNA. In the cDNA template, the primer would be a continuous exon sequence whereas in the DNA the primer would be divided by an intron. You can confirm actual amplification of cDNA sequence later on, as the primer won't anneal to contaminating DNA because the intron will interrupt the primer.
Follow normal primer design parameters besides intron placement. In other words, you want to avoid a sequence that will anneal to itself (form hairpin loops) or that will bind with the other primer (form primer dimers).
Design primers so that they are from 18-30 nucleotides long, with a melting temperature between 45-65 degrees Celsius. Avoid long repetitions of bases and choose a sequence with a G-C content of 40-60 percent. Make sure your 3' (three prime) end is not too heavy in Gs and Cs to prevent multiple site priming.