This study proposes a combined infill pattern design that is not currently available in standard slicing software. The novel design is described in detail to enhance mechanical performance compared with conventional infill strategies, i.e., rectilinear and concentrated patterns. The paper evaluates the effectiveness of combining different infill patterns by tensile testing. In the paper, a carbon fiber-reinforced PLA, which remains underexplored as compared to standard PLA materials, will be used for studies. The impact of key process parameters, including infill pattern, infill density, and printing speed, on tensile strength is systematically investigated by using the Taguchi method. Results indicate the proposed pattern provides improved strength under the same printing parameters and conditions. A combined infill pattern design makes the printed parts stronger and less brittle across all infill densities. For tensile-strength influence analysis, infill density has the greatest effect. The infill pattern is the next most important factor, while printing speed has the least impact. Besides contributing a novel infill pattern to improve mechanical performance, the paper provides a validated methodology for parameter optimization in fused deposition modeling using carbon fiber-reinforced PLA and offers valuable analysis to enhance structural integrity in additive manufacturing applications.