It helps to close your eyes, and imagine it happening. Then, write down everything that happened. Things like whether or not the person's sweating, if their worried, angry, sad, if their cold, hot. Every detail is important.
You just have to relax, take your time, and let the words flow.
Hehehe, it's hardly something that has a lot to do with experience. Being a truly good writer is just something that comes natural. Although, that's not to say a little practice can't make you improve.
If you love reading, and have a fairly decent imagination, then writing shouldn't be a problem at all. However, if you don't like reading the occasional book now and then, and prefer a video game, or a movie instead, then writing is not a path you should choose. Not unless you have a certain fancy for the written word.