I would not attempt to go on your own; if you don't have a walking partner, it's possible to go with one of the organised trips and a guide.
The weather can be so changeable as you climb, so prepare for all weathers. Take plenty of layers and have some spare with you, a scarf/buff, hat and gloves, as well as waterproof trousers and jacket - decent walking boots are a must. Have a backpack with plenty of snacks and water, as well as fist aid supplies.
Some find it helpful to take walking poles - I certainly used them to dig into the ground on one of the more exposed corners or I would have been blown over!
I went in September and although it had been a very hot summer, there was still a lot of snow even before we reached the summit, it was -11c at the top and the wind chill made it feel a lot colder!
Although there's phone signal, it can't be relied upon for online maps / gps / calls, as the extreme cold can make some phones shut down.
Leave early, take your time and stay safe. It is a worthwhile experience, but challenging, so make sure you do some training beforehand.