To use basic formulas:
1) Start with ohmic resistance (R) in your signal path. Or estimate it as voltage divided by Amperes.
2) Calculate C to obtain an RC combination with the same rolloff frequency as your desired notch frequency.
3) Similarly calculate L to obtain an LR combination.
4) Make a tank circuit with values L & C. (This creates a resonant frequency which should equal your desired notch frequency.)
To get the steepest notch, you want high Q. To improve Q, minimize ohmic resistance in the tank loop. If the notch is too shallow then it should help if you increase L:C ratio.
Typically L is 100 to 100,000 times the C value.