There is a strong and growing movement (often referred to by the acronym FIRE: financial independence/retire early) which can be an excellent source of encouragement and education in this regard. My personal .02 on the matter goes something like this:
1. As mentioned before: invest EARLY and often, preferably within a tax deferred IRA or equivalent, taking advantage of employer matches first. There is tremendous power in the time value of compounding
2. Ditto again: for most investors, low-price equity index mutual funds are the best route. They beat a managed approach more than 75% of the time, and without all the costs. I also like Vanguard. For logical and very rational individuals, stock picking or the like may work.
3. Try to create a source of passive or semi-passive income early on. Many are impeded in leaving employment by loss of associated health care benefits, or the reality of bridging the gap between your actual retirement and age 59-1/2 when one can access one's IRA. If you have a goose regularly laying golden eggs without your being on-site, this becomes a math problem, nothing more.
4. Play good defense: Simplify, downsize, and eliminate debt. Losing a payment or an expensive-to-maintain luxury is like getting a raise of that same dollar amount. Remember that free time is a luxury in and of itself, and one you can never get back once its gone.
5. I don't like the work "retirement". Implies quitting or letting go, or disengaging. A dear and wise friend instead calls his situation "re-wirement". He believes it remains critical to stay engaged socially, with some meaningful work, to truly stay healthy. Service or volunteer work is a tonic for the soul. Start that business you always dreamed about, or take that course! Just don't plan on spending all your time golfing, fishing, traveling, etc. (as fun and important as those may be to you) once you leave the rat race or you will soon be breathing your own fumes. Note to self: nobody wants to hear the details of your latest European vacation for the entire evening together.
6. The earlier one quits conventional work, the longer the retirement period and thusly lower safe rate of withdrawl from one's retirement nest egg. It's also increasingly important to maintain a higher percentage of equity investments (vs. bonds, CD's, etc.) even in retirement. My personal plan: 3.5% SWR and 75% equities, at least until 70 y.o. It's also wise to plan ahead to avoid having to sell equities to fund early retirement in a declining market.
7. Due to the big hit incurred in reserving a % of a pension to a spouse, it can make more sense to have the vested spouse take 100%, then buy a series of level-term life insurance policies instead: say 1-10 year and 1-20 year, overlapping for 10). Get hard quotes and do the math. Don't ever buy life insurance as an investment in itself, however. Ignore this advice altogether if the vested spouse is in poor health.
8. Invest in your physical, emotional, relational, intellectual and spiritual health. We can often improve our odds of lasting happiness, health, and prosperity with a few regular disciplines, which tend to snowball in a positive way.
Sorry for the very long post, and for including so much personal opinion. I surely don't have life all figured out but I've been working on this area for a while and my wife and I are now beginning the process of leaving the rat race at 55 y.o. One of the nudges has been the brand-new 2014 boat I own that barely has 100 hours cause I'm working all the time and never get a chance to use it. Last year we used our Summer home less than 20 days total. And it regularly breaks my heart to see patients of mine having their lives turned upside down in their 60's, or 50's, or even earlier, with a grim cancer diagnosis. I would love to hear input from others on this topic.
Cheers! Mike