Don't skip acclimatization
The mountain doesn't care about your fitness if you haven't allowed your body to adjust. Choose a 7-8 day route, not 5-6. Book Lemosho over Marangu. Acclimatization is time, not effort.
Don't carry cotton
Cotton absorbs sweat, dries slowly, and becomes dangerous when wet at altitude. Replace every cotton piece with wool, synthetic, or merino. Includes underwear and socks.
Don't wear new boots
The single most common trip-ruiner: new boots causing blisters on day 1. Break your boots in with 30+ hours of walking before arriving. If buying new, do it 3+ months ahead.
Don't overtrain in week 12
Panic-training in the final two weeks adds nothing and risks injury. Back off volume, maintain a few gentle hikes, eat well, sleep more. Arrive rested — not just fit.
Don't overpack
Porters limit you to 15kg of personal gear. Overpacking means things left at hotels — and excess weight they're carrying up the mountain. Pack disciplined: what do you actually need?
Don't drink alcohol at altitude
Skip every drink above 2,500m. Alcohol dehydrates you, disrupts sleep, and exacerbates altitude symptoms. Save the celebratory beer for Moshi on return.