Our group leader, Simon from the African Walking Company, was superb.
He was organised, approachable, calm, patient, enthusiastic, encouraging and had excellent English. He led his team of porters and guides very well. A true leader.
You might want to consider taking Diamax to help combat the possibility of altitude sickness.
The fitter you are, the easier it will be and the more you'll enjoy it. Try doing some hill walking in the Highlands, the Lakes or Snowdon before going. It will help build up your fitness levels.
Take warm clothing. While it is warm during the day it can get cold at night. We woke up to frost on several mornings. The ascent to the summit is done overnight, that does get cold. I'd recommend thermals for legs and upper body. In addition I'd suggest you have another 3-4 layers of warm clothing. On top of my thermal vest I had another vest, a warm shirt and a windbreaker then my jacket. Gloves, a balaclava and a hat were also used. On top of my thermal longjohns I had lined trousers designed for wearing in the Scottish winter. That kept me warm.
You'll be sleeping in tents so take a torch and a head torch. You'll need a head torch for the overnight climb to the summit. Make sure you take, or hire, a warm sleeping bag and good quality ground mat. The tents can get cold.
Take cash in US dollars. Moivaro Lodge, where we stayed before and after the climb, don't accept Sterling but do take US Dollars as well as Tanzanian Shillings. Take your US dollars in small denomination notes. Tips for the guides and porters are paid in US Dollars. Most shops, street traders etc accept US Dollars.
If you leave getting your visa until you arrive in Tanzania be prepared for delays. Try and be one of the first off the plane; first come first served. It's all a bit chaotic but they eventually get there.