1) Check your system. Your hood should snug down tight enough to seal out windblown rain, and your jacket’s hem should extend well below your waist. Make sure cinching your hipbelt or bending over doesn’t expose a gap.
2) Protect your feet. Reseal your boots before the trip, and wear water-proof gaiters under your rainpants.
3) Seal your sleeves. Hard rain can sneak in at your wrists. Shorten your trekking poles so your forearms angle downward, and avoid hooking your thumbs around your pack straps. Tuck baselayer cuffs under your shell to keep them from wicking water upward.
4) Keep gear dry. Use a pack liner (or trash compactor bag) and/or waterproof stuffsacks. Add a pack cover to keep water weight down.
5) Avoid overheating. Even in cold temps, you’ll sweat while working hard in a waterproof jacket. Wear only a light baselayer under your shell and moderate your pace to stay cool.
6) Carry an umbrella. There’s no better or more breathable protection (unless it’s really windy). Rig it to your pack with a stick and duct tape.
7) Be realistic. After consecutive days of hard, steady rain, getting wet is inevitable. Hike in your damp clothes, and save dry stuff for camp.