It's officially fall and as the days grow shorter, waists are growing thicker. Though Dr. Phil may have a few kind words for dieters, most experts agree the two keys to keeping the kilograms in check are portion size and setting small goals.

So what's this got to do with investing? Plenty, as a matter of fact.

Absentmindedly snacking on chips is just as detrimental to your diet as gorging on new cars, ATM fees, and daily lattes (even skim) is to your future savings. When you don't track your cash flow -- it's all about portion control -- the bills add up and the savings resolve dwindles. (FYI: That small grab bag of Fritos you get with your Subway sandwich has 2.5 servings.)

Don't deep freeze your spending all at once, though. The key to dieting and investing is to set achievable milestones along the way so that you don't slip back into old habits. For example, if spending less at restaurants is a goal, instead of making your family choke down mac and cheese each night, simply cut back your dining out once a week for the first month. Next month add another eating-in day a week.

What to do with the extra savings? Sock away some for a little treat (hands off until you reach a goal!), and put the rest to work for saving for a chocolate-covered future. For short-term cash, don't play it too risky. A certificate of deposit or money market fund is as fancy as you need to get.

If the "buddy system" works better for you, grab a financial workout partner (how about the one who shares your roof?) and come up with the short-term steps that'll provide your svelte selves a fat-cat retirement. And if you need a gentle-handed drill sergeant to hone your form and inspire some discipline, consider hiring a professional financial advisor -- or joining our TMF Money Advisor service -- to find out just how many bags of Fritos you have to pass up to retire in style.