step on, trample, practice, carry through
踐 centers on the physical act of stepping or trampling, and extends to the idea of carrying out an action in practice, as if treading a path.
踐 combines 足 (foot) with 戔, which likely contributes the sound and the idea of treading or trampling. The exact historical development of 戔 is uncertain.
The left side 足 means foot, and the right side 戔 looks like a pair of halberds (戈) over a small object. Imagine a foot trampling over a field of weapons, practicing a warrior's path.
For セン, picture a foot stepping on a cent (coin) on the ground: cent -> セン, and the foot tramples it.