I think some of the advice here is quite good, but especially given the title of your question, someone has to point out that there's literally a book on the subject called "How to Stop Worrying and Start Living," by Dale Carnegie.

It's a good book. It probably won't solve all your problems without you needing to do some inner work, and I generally recommend meditation as a way to find peace, but also you should read the book since it directly answers your question :)