Before you take on any kind of home renovation project, you need to think about what you're going to get out of it when it comes time to sell your home -- whether that's a month from now or five years from now.
No matter when you plan on selling your home, here's how to measure the true value of your renovation:

1.  Don't always think in terms of dollars and cents
Instead of worrying about getting every penny back on that $5,000 you spent in your master bathroom, think about the other rewards that bathroom can bring you -- like being able to sell your house in less time.
A buyer may not be willing to spend an extra $5,000 on your house just because you renovated the bathroom.  However, they may walk into your luxurious, spa-like master bathroom retreat and fall head over heels for it -- and decide that they've absolutely-positively-gotta-have your home.
Remember, the longer your house sits on the market, the lower its chances of getting the full asking price.  Plus, you'll have to keep making mortgage payments, paying homeowners' association fees, and homeowners' insurance premiums the entire time it's on the market.  If you can get rid of all that responsibility sooner rather than later, your renovation really did pay off!

2.  Think about the maintenance
If you add something to your home that requires a lot of extra maintenance -- like a pool -- potential buyers may actually consider it more of a liability than a luxury.  After all, if the buy your home, they'll have to deal with keeping the pool clean (or paying someone to do it).  If that's not something they want to deal with, it can actually prevent them from buying your house altogether.  So much for getting a return on your investment!
And, remember, until you sell the house, you'll have to deal with all of the maintenance yourself -- on top of the initial expense.  So, if the pool costs $10,000 to build and $100 per month in chemicals and other maintenance, you'll have to figure that monthly expense into your budget.

3.  Look at it from the buyer's perspective
You may not necessarily think of roof repairs as an "upgrade"(at least, not in the way you think of granite countertops and stainless steel appliances).  However, those roof repairs represent one less thing a buyer has to deal with.  Now, he doesn't have to move in an address the roof problems.
That convenience alone can make your house stand out ahead of all the other nearby houses for sale!

4.  Don't assume you have to spend a ton of money in the first place
That investment you're trying to get a return on doesn't have to be money.  It can also be time.
If you skip the expensive renovation projects and simply spend a few days with your sleeves rolled up, clearing out all of the clutter in your house, it can make a much better impression than any fancy kitchen or modern bathroom.
In fact, some good ol' fashioned de-cluttering can show off the natural beauty of your home, which will make it easier to sell.  
And best of all, it can help you fetch your full asking price -- all without spending a dime!  Now THAT'S time well-spent!