1)
What is the meaning of "Pe'amai Hachen"?
1.
Radak: Accustom me and guide me in Mitzvos Aseh, and do not give to the Yetzer ha'Ra power to rule over me, and I would transgress a Lo Sa'aseh.
2.
Malbim: Hashem's word and His commands guard his steps, so they are proper not to stumble due to the Nefesh.
2)
Why did he say "v'Al Tashlet Bi Chol Aven"?
1.
Radak: This is like "Gam mi'Zedim Chashoch Avdecha" (refer to 19:14:2:2). "Chol" includes even a small Aveirah.
2.
Malbim: Via Hashgachah, guard me from being trapped.
