Image: Couple with For Sale sign in front of house © Jupiterimages, Brand X, Getty Images

You might be tempted by low interest rates and a weakened housing market to buy your first home this year or to move up from your current house.

But getting a mortgage is tougher than it was just a few years ago. Lenders are pickier about all facets of the process, including:

•Your credit scores.

•The size of your down payment.

•Your income and how steady it is.

•Your other debts.

•The value of the property versus how much you want to borrow.
Here's how to get into the best possible shape to land a mortgage today:

1. Burnish those credit scores

Mortgage lenders typically pull FICO credit scores from each of the three major credit bureaus (Equifax, Experian and TransUnion) and use the middle score to help determine your rate and terms. If you're a couple, a set of scores will be pulled for each of you, and the lower of the two middle scores is typically used.

These days, you need a 740 middle FICO score to get the best deals. If you fall much below that, you'll pay more.

Liz Weston

Liz Weston

Someone in the 700-720 range, for example, might get an interest rate that's a quarter-point to half a point higher than someone with better scores, says Cameron Findlay, the chief economist for mortgage quote site LendingTree.

The costs climb as your score sinks, and many lenders these days have a cutoff point around 600. Below that, they won't even consider you, so you might have to shop for a lender that will.

The Federal Housing Administration's minimum score is 580 if you want to put down the minimum 3.5% down payment. Below that, you'll need 10% down.

The fastest ways to boost your scores are to correct any serious errors in your credit reports (AnnualCreditReport.com is where you get your free look) and pay down your credit card debt. For more, read "Raise your credit score to 740."

2. Be a worker bee

The days of "liar's loans" are gone. Now lenders want proof of steady income. Ideally, you've been working at the same job for two years or more and have the W-2 forms to prove it. Lenders want to see two years' worth of tax forms, as well as your most recent pay stubs.

Any other income with a two-year history, such as investment income, alimony or disability payments, can be counted when lenders determine how big a mortgage you qualify for.

If you're self-employed, prepare to jump through more hoops. You're likely to be asked for more documentation of your income, including business tax returns, a profit-and-loss statement, copies of your business license and even a letter from your accountant.

What if your work history is spottier? Say you lost a job in the recession and had to take one at a lower salary. That doesn't knock you out of the running for a mortgage, but the amount you can borrow will be based on your new, lower pay.

3. Keep your debts low

Most lenders have moved back to old-school ratios, whereby your mortgage wasn't supposed to exceed 28% of your gross monthly income and your other debts no more than 8%, for a total debt-to-income ratio of 36%.

You can get a mortgage with higher debt loads, but you might pay a higher interest rate. If your debt-to-income ratio exceeds 45%, you'll typically need high credit scores and lots of cash in the bank to persuade a lender to go along. Above 50%, you might be out of luck.

When figuring your debt load, lenders typically factor in only the minimum payments on your credit cards and other loans.

If you have credit card debt at all, you're probably not ready to be a homeowner. Credit card debt indicates you're living beyond your means, and buying a home is likely to make that worse. Develop the discipline to pay off your cards, and you'll be in better shape to buy a home.

4. Bring some cash to the table

The 20% down payment is once again king. Put down less than that, and you'll have to buy private mortgage insurance, which will increase your monthly payments.

Many people with less than 20% are being funneled into FHA loans, which come with higher rates than conventional loans but offer you the option of putting as little as 3.5% and saving any extra accumulated cash.

Talk through the possibilities with your loan officer, as a smaller down payment could result in a higher rate but more overall financial flexibility, since you'd have more cash left over after closing to cover emergencies, maintenance and repairs.

I believe a 20% down payment is the smartest way to go, if you can swing it. But I also think it's wise to have a good pile of cash left over after you buy a home, because you're going to need it. For more on this, read "Your first home? Save for repairs"

5. Get real about the house's value

In Econ 101, you might have learned that fair market value is the price a willing and knowledgeable buyer would pay a willing and knowledgeable seller when neither is under compulsion to buy or sell.

In today's mortgage world, however, the value of a house is what the appraiser says it is, and I'm hearing a lot of complaining that appraisers have gotten pretty conservative.

Why does this matter? If the appraiser says a house is worth less than what you agreed to pay, you'll have to cough up more money for the down payment to make up the difference or go back to the negotiating table with the seller (as if it weren't torture enough the first time around).

Protect yourself as much as possible by thoroughly researching sales of comparable properties before you make your bid. Your real-estate agent should be able to help.

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There are other ways your mortgage deal can go south, even if you try to get your financial and credit situations in the best possible shape.

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.