Ben Nevis sounds like a mysterious place when you are planning a hike. I remember reading you need good orientation skill, be prepared for snow and not go if you are not experienced. Well, it is not true. Not really.
Get a map if you want, but you do not really need it. Start from Glen Nevis visitor centre, cross the bridge and go up the mountain track or start from Glen Nevis Youth Hostel to join the track. There is really only one way up. You can notice a different path when you get to the first lake, but ignore that and continue up the mountain. You can´t get lost and especially if you go during the summer as it will be busy. It takes about 3-4 hours to get up and then about 2-3 hours to get down, depending on how skilled and fit you are. Also, there is a lot of water on the way which can get slippery, so be careful and wear appropriate shoes.
The actual hike is not one of the easiest one. If you sit around in your office all year long and do not exercise, avoid going to Ben Nevis. But if you hike at least from time to time, or even if you just move and exercise enough, it will be ok. The whole hike is as if going up the stairs, so if you live in a building without a lift, you won. Check the weather forecast before you go but also look at the sky and trust your feeling. The Scottish weather is very unpredictable. The day I was going to Ben Nevis it was supposed to rain in the afternoon but the sun was shining brightly when I was on my way down. I would avoid going during winter since it gets really cold up there and you might find snow, unless you are really experienced. In that case, you will be ok. Don´t forget to take a jacket and wear waterproofs.