Thinking too much can take up a lot of your time. And leave you with no time for other things.
Of course you should think before you act. There's nothing wrong with planning either. Just don't become the person who only thinks and plans.
Don't wait for the time to be perfect, it never will be. Don't plan for every problem that could arise, you'll never be able to cover it all.
Stop thinking and do what you need to do. The more you put things off, the worse the procrastination will get. Make it a habit to spend more time doing.