it is recommended that you use serial dilutions of your cDNA sample. First you have to optimize your working concentration for QPCR. Dilute them in 1:10 to make 4 or 5 dilutions. Check which dilution is giving you the best result. If you don't want to use dilutions then use standard 1ul of cDNA for QPCR.

I typically use 10 ng of cDNA per well for my qPCR (assuming 100% efficiency of the reverse transcription reaction). This amount works well for robust or moderately expressed genes. More lowly expressed genes may require you to add more cDNA to ensure reliable detection by qPCR.

I use 1 µg of total RNA (treated with DNase) for my cDNA synthesis and dilute the reaction 5-fold upon completion (e.g. 1 µg RNA/cDNA in a 20 µl reaction gets diluted to 100 µl). I then add 1 µl of the cDNA (now diluted to 10 ng/µl) per well in my qPCR.

I would check the concentration and quality of the cDNA and dilute from there. Remember to account for increases or decreases in fold change if you're expecting them.