1. Figure out what you want early, then work as hard and often as you can to get to that place professionally and financially. You can then take it easy afterwards, enjoying the fruits of your labor in a career that compensates you well and comes easily / largely stress free. This is because you'll never be as full of energy and as sharp as you are in your 20's. Use every last drop of that energy and ambition now. Drive hard in the paint ages 22 - 29 so that you can chill, vacation, and save lots in your 30's and 40's.
2. Speaking of saving, as others have said, it's important to start early. Even if you can only afford a few % of each check to be diverted into retirement or a regular savings account. Get to saving as early as possible.
3. Don't fuck up your credit. If you can't afford something then don't finance it. Always pay your credit card bills / loans on time. In fact strive to be debt free by 29. One of the best things I ever did for my sanity and general well being was paying off all of my debt just before my 28th birthday. Haven't had so much as a car loan since. I pay my credit card(s) off every week or immediately after a large purchase (for those rewards baby).
4. Don't dwell on what others think. I know it's hard not to want to be trendy or keep up with the Joneses when you're really young, but seriously, fuck what people think. If you can't afford a nice car then proudly drive that old hoopdee. You want to save money and live in a trailer park for a few years, then go live in that cheap trailer and stack your chips.
5. Set aside some time each year to get away for a week. Ideally with a loved one. You don't have to go to <trendy city A> and stay in <five star hotel>. Just escape some place for three to five days. Don't check work email. Don't respond to texts or tweets. Such little escapades go a long, long way in giving perspective on just how little most stuff actually matters at the end of the day.