This work presents how the optimization of polymer conductive composites constituting the semi-crystalline polymer matrix (low-density polyethylene (LDPE) and isotactic polypropylene (it-PP)) and carbon black (CB) by melt-mixing process, has an important influence not only in diminishing the resistivity of the composite but also in reducing the critical concentration of CB. The experimental procedure consists of studying the influence of processing parameters such as mixing temperature, time, and speed on the electrical resistivity values. Optimal parameters are considered as those obtained with the lowest standard deviation for electrical resistivity and a reduction in resistivity in comparison with the arbitrary conditions established as preliminary or reference. The control of those parameters allows in attaining an important reduction (7%) in the critical CB concentration at threshold percolation in both the studied composites in comparison with those obtained under unfavorable conditions or even with those obtained under reference conditions.