Just start doing it. I would start writing a regular journal every morning maybe...don't be concerned about how it reads to start, just go on pure inspiration. Then maybe do small book reports for yourself, your thoughts on a newspaper article.
Then maybe check out some writing forums that give prompts and start writing using those.
And don't be concerned about how good or bad it is, it's not about quality writing at this point, it's about simply writing.
And good luck!