Trouble is, I don't know any writers who do! Unless you're writing an autobiography, chances are you will have to write about something you don't have personal experience with. If you're writing sci-fi or fantasy (my two favourite genres), then you really can't get by without it. There will be magic, swordfighting, space travel, and who knows what else.
In Reckless Rescue, aside from the obvious space travel, I had an unexpected unknown – snow. Here in Australia, especially in sunny Queensland, we don't see much snow. It has, on a very rare occasion, snowed in Toowoomba, about a two hour drive away, and the Snowy Mountains are about 12+ hours away.
What I'm trying to say is that I've never seen snow. And there is a lot of snow in Reckless Rescue. Marlee's planet has a very harsh winter, where being snowed in, blizards and frostbite are all very real dangers.
So how do you write about something that you have no personal experience with?
It's all about the research.
The first port of call is your old friend Google. I managed to find astronauts descriptions of what takeoff felt like, the risk factors for frostbite, what it felt like to be burried in snow, and what sort of plants will survive the cold.
When that fails, I turn to forums. I like NaNoWriMo for this, especially during November, but the site is still active (albeit quieter) at other times of the year. There is a huge range of people with very varied experiences there, and chances are, someone will have an answer for you, or an idea of where to look for one.
How about you? What things have you had to research for your writing? What other places can you look for the answers?