Budget the Luxuries First!
Strictly speaking, his advice was preceded by another Heinlein maxim as well. "Sovereign ingredient for a happy marriage: Pay cash or do without. Interest charges not only eat up a household budget; awareness of debt eats up domestic felicity." Today, that advice gets abused eight ways to Sunday, as the average household is currently carrying credit card debt to the tune of over $10,000. Assuming an interest rate of 18%, this works out to about 150 bucks a month going to the credit card company. That's money NOT available for things like fresh flowers on your desk... new skis... upgrading to gourmet coffees and wines for daily consumption, or dinner out (including tips and babysitter).
Luxury item #1: Get out of consumer debt
Being debt-free is an incredible luxury! There are a ton of books and articles out there already on how to budget and avoid debt, so I won't hold forth on how to do it. The important issue is WHY to do it. And the answer is simple. Peace of mind is the ultimate luxury!
Luxury item #2: Make some time to make a wish list!
While putting the wheels in motion on reducing debt, there's a happier issue to think through as well: What is it you really want out of life? Peace of mind (and of household) starts with asking these Really Big Questions!
More importantly (assuming you actually care about your relationship), what is it your partner craves? If you don't know, well... it can be fun finding out. Too many financial planning exercises are painful, which is why not enough people do them. This exercise, finding out what really matters to you both, isn't.
What are the things in life that really feel like luxury to you? Now is the time to identify them, and separate out the smaller, less satisfying things you're paying for that keep you from getting what you really want.
To keep to the spirit of fun, I've found it's useful to agree to some simple ground rules:
Make some unbroken wish list time for the two of you
There are no such things as 'silly ideas' or 'waste of money' items during the wish list time (that will come later on during a reality-check period)
No impulse spending during the wish list time! Window shop if you want, share a seat in front of the computer if you're looking online... my preference is to go hang out in antique markets and bohemian shopping districts for ideas, but you might prefer to go visit a travel agent's office or web site. It DOESN'T matter!
Each partner gets equal time to show off their ideas if they want it.
Being realistic, there will, of course, be a price tag associated with the wish list. Also being realistic, not all luxuries cost an arm and a leg, either. If you have the iron will to make a strict budget and do without so that you can go hang out in Tuscany for a month next fall, good for you (and yours!) If you're like me, though, it may make sense to make do with lesser luxuries.
Luxury item #3: Keep looking until you find reasonably-priced luxuries that really make your life more worth living, then revel in them!
That's all it takes. If you get this far, you've done a few extremely healthy things. For starters, you've actually talked to your sweetie about money, without it being a crisis! You've spent some time dreaming together. You've examined your debt and thought about what it's costing you. And with any luck, you've found at least one thing you can enjoy without feeling guilty about what it's costing you... because it's an investment in your piece of mind.