Prioritize
Try getting out a pad and paper and writing what you absolutely have to do today. Writing out your tasks-at-hand simplifies your thoughts and gets rid of all the mental chaos and stress. This will allow you to prioritize and figure out what needs to get done soonest. Ideally, you'll be able to start working on that as soon as you figure it out.
Broad view
Think about the big picture. This seems counterintuitive if the goal is to simplify, but it's actually important. Think about what you really want and where you really want to be in your life, and start weeding out anything that doesn't jell with those ideas. For example, if you're finding that there aren't enough hours in the day to do everything you want, cut out TV and make sure you're not oversleeping.
Narrow down
After you've zoomed out and put things in perspective, go back to the details. If you change a tiny part of your life each day for a year, by the end of the year the big picture will have changed completely. Implement small changes, one at a time, the goal being simplicity. Shave off an unnecessary expense, simplify your diet, etc.
Relax
Don't procrastinate, but relax. Take things as they come. There's no point in simplifying your life if the process just stresses you out. Look at it as a gradual process rather than an instant gratification. De-cluttering your surroundings will eventual help you de-clutter your mind.
No multi-tasking
One thing at a time. Pick a thing, and do it with deliberate hard work instead of half-assing 5 things at once. If you have to clean your desk, clean your desk. Don't clean a little, eat, clean a little, check facebook, clean a little, write emails. Just do it; you'll feel the satisfaction of dedicating your full attention to something.
Give
Much of the unnecessary complexity in our lives comes from having too much stuff. We accumulate stuff over time and sometimes we keep it just for the sake of having more stuff. Look at all your stuff and categorize it.
-What do you need?
-What did you want when you bought it?
-What do you still want?
-Who could use the stuff you don't want anymore?
Then give stuff away, or sell things. eBay and craigslist are awesome reminders that "one man's trash is another man's treasure." Drop by Goodwill or another charity. It'll be a load off your mind and another step toward simplification.
Moderate
Basically, shop and live mindfully. Be honest with yourself about what you need and try to stick with the basics. We all have a friend (it might even be oneself) who uses shopping as an opiate and loses themselves in a sea of clothes racks, receipts, coupons and credit cards. Avoid that like the plague. If you are a 'shopaholic', take little steps to work your way back to basics.
