Sensors based on surface plasmon resonances (SPRs) have proven themselves as promising devices for molecular investigations - still there is potential to determine the geometrical parameter set for optimal sensing performance. Here we propose a comprehensive design rule for one-dimensional plasmonic grating structures. We present an analytical approach, which allows for estimation of the grating parameters for best SPR coupling efficiency for any geometry and design wavelength. On the example of sinusoidal gratings, we expand this solution and discuss numerically and experimentally, how the grating modulation depth can be refined to achieve optimal signal resolution. Finally, we propose a benchmark factor to assess the sensor performance, which can be applied to any sensing scheme utilizing resonances, allowing for comparison of different technological platforms.