You can go any time of year, but October to April is high season. Be prepared for crowds and make your reservations and travel arrangements in advance. Spring is a good time to go. The weather is warming, the flora is blooming and there aren't that many tourists yet. Any time of year, you will experience wind, so you will need warm clothing. No need to dress for an Artic expedition, but you will need a windproof jacket, hat, gloves, sturdy hiking boots.
You will need a lot of film for your camera! Use polarizing and UV filters for the glaciers.
If you plan to camp, you can do so at a camping grounds on Peninsula Magallanes. You will need your camping gear of sleeping bag, portable stove and cooking fuel. Take plenty of water. If you plan to use a shelter, a refugio, you'll need only your sleeping bag.
Take a backpack with you for your incidentals and make sure you have water and snacks. High energy ones are good. You'll find lots of food stores and restaurants, but be prepared for the cost. Everything has to be brought in from miles away.